Anatomy of crocodiles

Vethacking.com @ BVSc,UZ-ATV100 Revision notes

 Introduction
• Crocodiles are sturdy lizard-shaped aquatic reptiles of the order
crocodilidae.
• There are 22 species crocodiles which are remarkably similar.
• Are subdivided into three families,
• Alligatoridae (the caimans, Caiman, Palaeosuchus, Melanosuchus, and
alligators Alligator)
• Crocodylidae (‘true’ crocodiles, Crocodylus and dwarf crocodile
Osteolaemus)
• Gavialidae (the Gharial Gavialis and False Gharial Tomistoma)
• There are two common species of crocodiles, the saltwater or estuarine
crocodile, Crocodylus porosus and the freshwater crocodile, Crocodylus
johnstoni.

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 Introduction
• With the birds, they are the only surviving archosaurs, the group
which included the dinosaurs.
• These large amphibious and carnivorous reptiles inhabit tropical and
subtropical lakes, rivers and coasts.
• They lay their eggs in nests constructed on land.
• Their morphology and physiology have been shaped by similar
lifestyles, allowing many generalisations about the group of
crocodilians as a whole

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Crocodilians

Crocodylus porosus
(Crocodylidae): the salt water
crocodile shows pronounced sexual
dimorphism, as seen in this male
(left)
and female resting on the shore.
[G. Grigg]

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Crocodilians

Crocodylus porosus (Crocodylidae): when feeding in the

water, this species lifts the tail to counter balance the head [G.
Grigg]

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Crocodilians

Crocodylus porosus (Crocodylidae):

the snout
is broad and rounded,the teeth (well-
worn in this
old animal) are set in an irregular row,
and a
palatal flap closes the entrance to the
throat

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Crocodilians

Crocodylus johnstoni
(Crocodylidae): the eyes and
the slit-like ears are
set high on the head, and can
be closed during
diving;G.grigg

MAGEJA.T@VETHACKING.COM.REVISION NOTES
General morphology
• Crocodilians are sturdy lizard-shaped reptiles, with a well-armoured head
and trunk and with horny skin and scales, reinforced with bony plates
• In modern Crocodylia, at least, the head is generally flattened and the
snout elongated.
• The nasal capsules lie near the tip of the snout, and nostrils which can
close in the external nares tend to be raised above the tip of the snout;
thus submerged crocodilians are inconspicuous when drifting toward
terrestrial prey.
• Members of the Alligatoridae tend to have broad snouts, whereas those of
the Crocodylidae range from broad to long and slender
• In gavialids the snout is extremely slender

MAGEJA.T@VETHACKING.COM.REVISION NOTES
General morphology
• Crocodilians have laterally compressed tails, webbed hind feet, and
the nostrils, eyes and ears are placed high along the head and snout,
all consonant with aquatic habits.
• Skull and jaws are solid and together with the strong peg-like teeth
can maintain an effective hold on prey.
• The palatal flap, a rigid plate of tissue at the rear of the oral cavity,
closes the posterior buccal space (oesophagus and glottis) against the
entry of water.
• A well-developed hard palate permits ventilation from nostril to
glottis, bypassing the mouth
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General morphology
• The nostrils can be closed tightly during submergence.
• Adult crocodilians are large and species show an enormous size range.
• The smallest are species of Palaeosuchus and Osteolaemus which grow to an
adult size of 1 to 1.5 m.
• Males of Crocodylus porosus more than 7 m in length and weighing perhaps 2000
kg, are the largest of the extant reptiles.
• Crocodilians show a pronounced sexual dimorphism.
• Males grow larger and often more rapidly than females, even though they attain
sexual maturity at an equivalent age
• Apart from size, there is no external indication of sex.
• The alimentary, urinary and reproductive systems open to the exterior via the
midventral longitudinal slit of the cloaca.

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Integument
• The skin is covered with keratinised scales, or scutes, many of which are
reinforced with bony plates, or osteoderms.
• Osteoderms are most prevalent in the dorsal and nuchal scutes which
commonly bear conspicuous ridges, and in the belly scales of some species.
• The nuchal, dorsal and some of the rectangular and keeled scutes are
covered by hard, wear-resistant beta-keratin.
• Since they are vascularised, scutes are involved in thermoregulation
• The fields of scutes are embedded in the intermediate skin under a
covering of alpha-keratin which provides an important barrier to water and
electrolyte exchange.
• This facilitates the homeostasis of body fluids in a wide range of salinities
(Salt and Water Regulation).

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Integument
• Flexible skin covers the neck and the flanks, whereas the abdomen
and sides of the tail are sheathed in large, flat, squarish scutes
arranged neatly in rows.
• Crocodilian scales bear a pore that is generally thought to be sensory,
analogous to the lateral line of fishes.
• Higher densities of small scales around the head, particularly on the
upper and lower jaws concentrate this supposed mechanosensory
apparatus.
• Alternatively, the pores could be a source of a detergent-like or oily
substance (perhaps a modification of betakeratin) since mud seems to
flush off them easily in the wild.
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Integument
• The prominent paired gular and paracloacal integumentary glands are
everted at capture.
• The gular glands lie in ventral folds of skin at the angles of the jaw and
the paracloacal glands are embedded in the lateral walls of the
cloaca.
• Their holocrine secretions are primarily lipid.
• Secretions analysed from both pairs of glands in most crocodilian
species contain sterols, free fatty acids, triglycerides, steryl esters and
aliphatic alcohols and, commonly, hydrocarbons

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Muscular system
• The crocodilian muscles seem to follow the general tetrapod pattern
• The crocodilian muscles reflect the general short fibre phenomenon
• Jaw closing muscles appear to be much more massive than the openers
and the jaws of even of medium-sized specimens can be held shut
comparatively easily, especially when coupled with the leverage attainable
by grasping the snout.
• Much of aquatic propulsion depends on the axial musculature.
• However, terrestrial locomotion is effected by the muscles of limbs and the
associated girdles.
• Some ventilation is powered by the intercostals, but much of inhalation
reflects the contraction of the m. diaphragmaticus, a striated muscle that
connects the liver to the pelvic girdle

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Muscular system
• The muscles deltoideus clavicularis, scapulohumeralis caudalis and
teres major all lie together on the lateral surface of the scapula blade.
• Muscles are divided into groups.
• Forelimb muscles are split into extrinsic/intrinsic and forearm
pronators/supinators.
• Intrinsic muscles are further split into extensor/flexor muscles of the
shoulder, elbow and wrist
• Hindlimb muscles are divided into superficial/deep and then
dorsal/ventral groups

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Muscular system

Fig 1. Orientation
terminology used in muscle
description. Diagram of the
Crocodylus porosus
hindlimb
with terms used to describe
orientation.

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Muscular system
• The large superficial dorsal muscles of the forelimb are often
removed during the skinning process .
• It is therefore not possible to identify or model these muscles.
• These include the trapezius, latissimus dorsi, rhomboideus and
serratus ventralis cervicus.
• In the lower limbs, where muscles inserting into the manus and pes
are also severed during skinning thus three muscles in the hindlimb
cannot be identified.
• These include the flexor digitorum brevis, pronator quadratus and
extensor hallucis longus.

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Forelimb muscles
• Superficial extrinsic muscles .
• Pectoralis (PEC)
• This muscle originates by a fleshy attachment along the ventral midline of
the animal from the interclavicle and sternal ribs.
• It inserts by a tendon on the proximo-ventral humerus at the deltopectoral
crest.
• Its principle function is in shoulder and limb adduction.
• It is a very large sheet-like muscle that covers the entire superficial ventral
chest area.
• Deep extrinsic muscles
• Levator scapulae (LS) (collo-scapularis supericialis )

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Forelimb muscles
• This muscle's origin lies with the neck muscles on the lateral cervical
ribs.
• It inserts on the anterior border of the scapula by a fleshy attachment
which extends from the most anterodistal part of the scapula to the
glenohumeral joint and is largely obscured from view by the trapezius
which overlies this part of the LS .
• It plays a major part in drawing the shoulder anteriorly.

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Forelimb muscles
• Serratus ventralis thoracis (serratus posterior ; thoracic-scapularis
superficialis)
• This muscle originates from the trunk at the ventro-lateral ribs.
• It inserts by a tendon on the entire medio-posterior margin of the scapula.
• It is a broad but thin muscle involved in extension of the pectoral girdle.
• Costocoracoideus profundus
• This muscle originates in the trunk on the lateral margin of the first few ribs
and inserts at the ventro-posterior margin of the coracoid.
• Both attachment points are fleshy.
• This muscle is long but thin and lies deep to the pectoralis.
• It functions as a pectoral girdle extensor.

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 Fig 3. Fresh-tissue dissection
with muscles identified around
shoulder. Lateral view of right
shoulder region of Crocodylus
porosus (XCb Cp5). TM:
Teres major, DS: Deltoideus
scapularis, SHC:
Scapulohumeralis caudalis, DC:
Deltoideus clavicularis, CBD:
Coracobrachialis brevis
dorsalis, TLM: Triceps
longus medialis, TLL: Triceps
longus lateralis, TB1: Triceps
brevis 1.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
 Fig 4. Fresh-tissue
dissection with some
hindlimb muscles
identified. Dorsolateral
view of right hindlimb of
Crocodylus porosus.
FTE: flexor
tibialis externus, IT1-3:
Iliotibialis 1±3, IF:
Iliofemoralis, FMTE:
Femorotibialis externus,
GE: Gastrocnemius
externus, PP: Pronator
profundus, FB: Fibularis
brevis, TA: Tibialis
anterior.

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Muscular system

Fig 5. Three-dimensional model of forelimb musculature in Crocodylus porosus. Lateral view of the
right forelimb. MAGEJA.T@VETHACKING.COM.REVISION NOTES
Fig 6. Superficial extrinsic muscles of the forelimb. PEC: Pectoralis.
MAGEJA.T@VETHACKING.COM.REVISION NOTES
 Muscular system

Fig 7. Deep extrinsic muscles of the forelimb. LS: Levator scapulae, SVT: Serratus ventralis thoracis,
COCS: Costocoracoideus superficialis, COCP: Costocoracoideus profundus.
MAGEJA.T@VETHACKING.COM.REVISION NOTES
Muscular system
• Intrinsic muscles
• Shoulder extensors/flexors.Teres major (TM)
• This muscle originates on the disto-lateral surface of the scapula by a
fleshy attachment, and inserts via a long and well-defined tendon
onto a bony ridge on the proximo-lateral humerus.
• TM makes up the postero-lateral surface of the scapula and lies deep
to the latissimus dorsi.
• It is involved in shoulder abduction, and also flexion to a minor
degree.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Muscular system
• Deltoideus scapularis (DS) (scapular triceps )
• This muscle originates by a fleshy attachment on the disto-lateral
scapula and inserts by a tendon on the dorso-lateral humeral head. It
is an elongate muscle that attaches to the scapula along its length
from point of origin until it becomes tendinous.
• It lies anterior to teres major.
• The DS acts as a shoulder abductor and flexor.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
 Fig 8. Intrinsic
muscles of the
forelimb:
shoulder
extensors and
flexors. TM: Teres
major, DS:
Deltoideus
scapularis, SHC:
Scapulohumeralis
caudalis, DC:
Deltoideus
clavicularis, CBV:
Coracobrachialis
brevis ventralis,
SC:
Supracoracoideus,
CBD:
Coracobrachialis
brevis dorsalis.

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Muscular system
• Supracoracoideus (SC)
• This muscle originates at the proximo-lateral coracoid by a fleshy
attachment and covers the entire humeral head.
• It inserts on the ventro-lateral humerus on the deltopectoral crest by a
fleshy attachment.
• The SC is very broad and triangular in shape, making up much of the
shoulder.
• It acts as a shoulder extensor and, to a minor degree, adductor.
• Scapulohumeralis caudalis (SHC) (teres minor )
• This muscle originates on the proximo-lateral and posterior scapula, and
inserts on the proximo-lateral humeral head.
MAGEJA.T@VETHACKING.COM.REVISION NOTES
Muscular system
• Both attachments are fleshy.
• It is a small muscle that is largely overlain by teres major posteriorly and
deltoideus scapularis anteriorly.
• The SHC functions as a shoulder abductor.
• Coracobrachialis brevis ventralis (CBV)
• This muscle originates by a fleshy attachment over the entire lateral
coracoid and inserts, also by a fleshy attachment, onto the deltopectoral
crest.
• It lies deep to the pectoralis and posterior to the biceps brachii. It is a large
and broad muscle that covers the lateral coracoid and proximo-ventral
humerus.

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Muscular system
• The CBV acts as a shoulder and limb adductor.
• Coracobrachialis brevis dorsalis (CBD)
• This muscle originates from the antero-lateral and proximal scapula
by a fleshy attachment.
• It inserts on the proximal third of the anterior humerus near the
deltopectoral crest.
• This muscle is triangular in shape and makes up much of the bulk of
the shoulder along with the supracoracoideus.
• It acts as a shoulder extensor and possibly also as a joint stabiliser

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Muscular system
• Subscapularis (SS)
• This muscle originates on the postero-lateral scapula by a fleshy
attachment and inserts by a fleshy attachment on the dorso-lateral
humeral head.
• It is a shoulder extensor and has also been identified as a shoulder
stabiliser due to its small size and limited mechanical advantage
• Deltoideus clavicularis (DC) (scapular deltoid )
• This muscle originates by a fleshy attachment on the antero-lateral
scapula and inserts on the dorso-lateral head of the humerus, again
by a fleshy attachment.

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Muscular system
• It makes up much of the bulk of the shoulder along with the
supracoracoideus, overlying most of coracobrachialis brevis dorsalis
as well as the insertion of deltoideus scapularis.
• It can sometimes be difficult to differentiate from coracobrachialis
brevis dorsalis and supracoracoideus.
• The DC acts to extend the shoulder.

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Muscular system
• Elbow extensors/flexors
• Humeroradialis (HR) (brachio-radialis )
• This muscle originates on the ventro-lateral humerus at the
deltopectoral crest by a fleshy attachment.
• It inserts with biceps brachii and brachialis on the proximo-medial
radius by a short tendon.
• The HR lies anterior to the biceps brachii and brachialis; it is also
broader than these other two muscles.
• It functions to flex the elbow.
• Biceps brachii (BB) (coracoantebrachialis)
MAGEJA.T@VETHACKING.COM.REVISION NOTES
 Fig 9. Intrinsic
muscles of the
forelimb: elbow
extensors and flexors.
TLL: Triceps longus
lateralis, TLM:
Triceps longus
medialis, ABR:
Abductor radialis, BB:
Biceps brachii, BR:
Brachialis, HR:
Humeroradialis,
TB1-2: Triceps brevis
1±2.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Muscular system
• This muscle originates on the ventral coracoid by a very long tendon
(half the length of the muscle belly).
• It inserts by a tendon onto the proximo-medial radius.
• This muscle is rather slender and is a major elbow flexor.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Muscular system
• Brachialis (BR)
• This muscle originates by a fleshy attachment on the anterior humeral
head.
• It inserts onto the proximo-medial radius with the tendon of the biceps
brachii.
• The BR is a thin and elongate muscle that attaches to the humerus along its
length.
• It lies between the biceps brachii and the humeroradialis.
• It is involved in elbow flexion.
• Triceps longus lateralis (TLL) (anconeus scapularis )

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Muscular system
• This muscle originates at the proximo-lateral scapula via a tendon,
superficial to the teres major and scapulohumeralis caudalis, but
deep to deltoideus scapularis.
• It inserts by a tendon onto the lateral olecranon process of the
proximal ulna.
• It makes up much of the dorsal surface of the upper arm and extends
over the medial surface of triceps brevis 1.
• This muscle's primary function is in elbow extension.
• Triceps longus medialis (TLM) (anconeus scapulocoracoideus)

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Muscular system
• This muscle originates by a tendon from the postero-lateral and
proximal surface of the scapula, deep to the teres major, and inserts
by a tendon on the olecranon process of the proximal ulna with the
triceps longus lateralis.
• TLM lies posterior to the triceps longus lateralis and is of a similar size
and shape.
• It is an elbow extensor.
• Triceps brevis (TB) (TB1 = Anconeus humeralis lateralis, TB2 =
anconeus humeralis medials, TB3 = anconeus major )
• This muscle is composed of 3 parts.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Muscular system
• TB1 originates by a fleshy attachment on the proximolateral humerus,
overlying the insertion of teres major.
• It inserts by a tendon on the proximal ulna at the olecranon process and
attaches to the humerus for part of its length.
• TB2 originates on the postero-dorsal and proximal humerus, while TB3
originates on the posterior humeral head.
• TB2 and TB3 insert together with TB1 also by a tendinous attachment.
• TB2 and TB3 run postero-dorsally along the humerus and sit flush against
the bone, attaching along the length of the muscle.
• TB1 overlies much of TB2.
• All parts of this muscle are involved in elbow extension.
MAGEJA.T@VETHACKING.COM.REVISION NOTES
 Fig 10. Intrinsic
muscles of the
forelimb: wrist
extensors/flexors.
FUL: Flexor ulnaris
longus, ECU:
Extensor carpi ulnaris,
ECRB: Extensor carpi
radialis brevis, ECRL:
Extensor carpi radialis
longus, FDL1-2:
Flexor digitorum longus,
FCU: Flexor carpi
ulnaris.

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Muscular system
• Abductor radialis (ABR) (humero-radialis internus)
• This muscle originates by a tendon from the disto-lateral humerus
and inserts by a fleshy attachment on the distal lateral radius.
• It runs along the lateral surface of the radius and attaches along its
length.
• It lies between the extensor carpi radialis longus and extensor carpi
radialis brevis.
• The ABR is an elbow flexor.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Muscular system
• Wrist extensors/flexors .
• Flexor carpi ulnaris (FCU) (humero-radialis lateralis)
• This muscle originates via a tendon at the disto-medial humerus and
inserts by a fleshy attachment at the ventral manus.
• It lies medial to flexor digitorum longus 1 and is a relatively slender
muscle.
• It is one of the major wrist flexors.
• Flexor digitorum longus (FDL) (flexor digitorum communis profundus )

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Muscular system
• This muscle is composed of 2 parts.
• FDL1 originates on the ventro-medial and distal humerus via a
tendinous attachment and inserts by a tendinous attachment into the
manus at digit 2 with FDL2.
• It lies between flexor carpi ulnaris medially and pronator teres
laterally, and is a relatively thin muscle.
• FDL2 originates by a fleshy attachment at the proximo-medial head of
the ulna before inserting via a tendon into the manus on the ventral
surface of digits 1-3.

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Muscular system
• FDL2 attaches to the ulna along its length.
• It is a thin muscle at its origin point but broadens substantially at the distal
ulna before thinning again and becoming tendinous.
• Both parts of this muscle are involved in wrist flexion.
• Extensor carpi radialis longus (ECRL) (extensor carpi radialis )
• This muscle originates on the ventro-lateral humerus by a tendinous
attachment and inserts, also by a tendon, on the dorsal manus.
• It is a long and relatively thin muscle that lies anterior to the abductor
radialis.
• The ECRL functions as a wrist extensor
• Extensor carpi radialis brevis (ECRB) (extensor carpi radialis profundus ;
supinator manus)
MAGEJA.T@VETHACKING.COM.REVISION NOTES
Muscular system
• This muscle originates with two heads which are almost
indistinguishable, one on the antero-proximal head of the ulna and
the other on the poster-proximal radius, both by fleshy attachments.
• ECRB then inserts at the dorsal manus via a tendon.
• The origin of this muscle
• lies deep to the extensor carpus ulnaris and abductor radialis.
• It is involved in wrist extension.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Muscular system
• Extensor carpi ulnaris (ECU) (humero-carpi ulnaris ; ectepicondylo-ulnaris )
• This muscle originates by a tendon on the disto-ventral humerus at the lateral
condyle and inserts at the dorsal manus via a tendon.
• It acts as an elbow flexor and wrist extensor.
• Flexor ulnaris longus (FUL) (humerodorsalis )
• This muscle originates at the disto-lateral humerus via a tendinous attachment.
• It runs along the lateral ulna and inserts by a tendon onto the dorsal
metacarpals.
• This muscle is wider at origin and thins towards its insertion point.
• It lies posterior to the extensor carpi ulnaris.
• The FUL functions as an elbow flexor and wrist extensor.
MAGEJA.T@VETHACKING.COM.REVISION NOTES
Muscular system
• This muscle originates by a tendinous attachment at the ventro-distal
humerus and inserts by a fleshy attachment on the ventral carpals.
• It attaches to the antero-medial radius along its
• length and lies between supinator anteriorly and flexor digitorum
longus 1 posteriorly.
• Its principal function is in wrist pronation.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Muscular system
• Pronator quadratus (PQ)
• This muscle originates by a fleshy attachment at the proximo-medial
ulna and inserts on the postero-distal radius.
• PQ is very broad at origin but thins towards its insertion point.
• It lies deep to the other ventral muscles of the forearm, between the
radius and ulna.
• It is an elbow pronator and also assists in stabilising the radius and
ulna.
• Supinator (SUP)

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Muscular system
• This muscle originates by a tendinous attachment at the disto-lateral
humerus and runs along the lateral radius, attaching to the bone,
inserting by a tendon on the antero-distal radius. It partially overlies
extensor carpi radialis longus at origin.
• SUP is a large muscle that lies on the anterior edge of the radius.
• It acts as the major wrist supinator.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
 Fig 11. Intrinsic
muscles of the
forelimb:
pronators and
supinators of
the forearm.
PQ: Pronator
quadratus,
SUP: Supinator,
PT: Pronator
teres.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Fig 12. Three-dimensional model of hindlimb musculature in Crocodylus porosus. Lateral
view of the
right hindlimb. The interactive version of this model is available in `Supplementary
Information'.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Muscular system- Hindlimb muscles
• Superficial dorsal muscles of the upper hindlimb.
• Iliotibialis (IT) (extensor iliotibialis)
• This muscle is made up of 3 parts.
• IT1 originates by a fleshy attachment from the antero-lateral ilium
and inserts via a tendinous attachment to the proximo-anterior tibia,
inserting with IT2 and IT3.
• It is a relatively slender muscle.
• IT2 originates by a tendon from the central lateral ilium between IT1
and IT3.
• It inserts on the proximo-anterior tibia via a tendinous attachment.
MAGEJA.T@VETHACKING.COM.REVISION NOTES
Muscular system- Hindlimb muscles
• It is a sheet-like muscle and is the largest of the iliotibialis muscles, making
up almost the complete dorsolateral face of the thigh.
• It is broad at the proximal end, thinning and narrowing towards its
insertion.
• IT3 originates by a fleshy attachment on the postero-lateral ilium and
inserts on the proximo-anterior tibia with IT2, also by a tendon.
• It lies directly posterior to IT2 and anterior of flexor tibialis externus.
• It is of a similar shape to IT1.
• The iliotibialis muscles make up the entire of the superficial dorso-lateral
thigh are all used in extension of the knee.
• Flexor tibialis externus (FTE)
MAGEJA.T@VETHACKING.COM.REVISION NOTES
Hindlimb muscles
• This muscle originates by a tendon from the postero-lateral ilium,
posterior to iliotibialis 3, and inserts via a long tendon, shared with
gastrocnemius externus, into the pes.
• The muscle body extends to the insertion of the flexor tibialis
internus muscles at the knee, beyond that the tendon continues by
stretching medial to the gastrocnemius externus to the final insertion
point at the proximal pes.
• The FTE is a large muscle that covers the posterior surface of the thigh
and acts as a hip extensor and knee flexor.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
 Hindlimb muscles

Fig 13. Superficial dorsal muscles of the upper hindlimb. ILFB: Iliofibularis,
MAGEJA.T@VETHACKING.COM.REVISION NOTES FTE: Flexor tibialis externus,
IT1-3: Iliotibialis 1±3.
Hindlimb muscles
• Iliofibularis (ILFB)
• This muscle originates by a fleshy attachment at the central lateral
ilium ventral to the origin of iliotibialis 3.
• It inserts on the proximo-lateral fibula via a tendinous attachment.
• The distal part of the muscle belly is visible between iliotibialis 3 and
flexor tibialis externus.
• It is a thin muscle that acts as a hip extensor and knee flexor.
• Superficial ventral muscles of the upper hindlimb .
• Ambiens (AMB) (pubofemoralis; sartorius )
MAGEJA.T@VETHACKING.COM.REVISION NOTES
Hindlimb muscles
• This muscle originates on the proximo-lateral pubis by a tendinous
attachment.
• It inserts on the proximo-anterior tibia at the cnemial crest via a long
tendon.
• This muscle is wide at origin, thinning as it becomes tendinous for
insertion.
• It is visible along the anterior surface of the thigh.
• Only a single head was identified in C. porosus.
• It is a knee extensor and hip flexor.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Hindlimb muscles
• This muscle originates on the proximo-lateral pubis by a tendinous
attachment.
• It inserts on the proximo-anterior tibia at the cnemial crest via a long
tendon.
• This muscle is wide at origin, thinning as it becomes tendinous for
insertion.
• It is visible along the anterior surface of the thigh.
• Only a single head was identified in C. porosus.
• It is a knee extensor and hip flexor.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Hindlimb muscles
• Flexor tibialis internus (FTI)
• This muscle is composed of 4 parts.
• FTI1 originates from the postero-lateral ischium and inserts on the
proximo-medial tibia via a long tendon with pubo-ischio-tibialis.
• It is a long and thin muscle.
• FTI2 originates by a fleshy attachment on the postero-ventral ilium and
inserts on the proximo-medial tibia via a tendon with FTI1.
• It is the largest of the 4 parts and is broad.
• FTI3 originates on the proximo-lateral ischium and inserts by a tendon on
the proximo-medial tibia with the other FTI muscles.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Hindlimb muscles
Fig 14. Superficial
ventral muscles of
the upper hindlimb.
AMB: Ambiens, PIT:
Pubo-ischio-tibialis,
FTI1-
3: Flexor tibialis
internus 1±3.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Hindlimb muscles
• It is broader than FTI1 and lies ventral to the secondary tendon of the
caudofemoralis longus.
• FTI4 originates on the latero-ventral ilium near the ischium and
inserts via a tendon with the other three FTI muscles.
• It is a small thin muscle.
• The FTI muscles are involved in hip extension and knee flexion.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Hindlimb muscles
• Pubo-ischio-tibialis (PIT)
• This muscle originates by a tendon at the postero-lateral ischium near
where the ischium and pubis join, and inserts by a tendon on the
proximo-medial tibia.
• It is a long and relatively thin muscle that lies lateral to flexor tibialis
internus 1.
• Its origin also lies between pubo-ischiofemoralis externus 3 and
adductor 1.
• The PIT is involved in hip extension and knee flexion; it also functions
as an adductor to a minor degree.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Hindlimb muscles
• Deep dorsal muscles of the upper hindlimb.
• Iliofemoralis (IF) (caudali-iliofemoralis)
• This muscle originates deep to iliotibialis 2 on the central lateral ilium
via a tendinous attachment.
• It inserts by a fleshy attachment onto the distal third of the dorso-
lateral femur between femorotibialis internus and femorotibialis
externus.
• The IF is tear shaped and attaches along most of the length of the
femur.
• It is one of the hip abductor muscles.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Hindlimb muscles
• Femorotibialis internus (FMTI)
• This muscle originates by a tendon on the dorso-proximal femur, distal and
anterior to iliofemoralis.
• It then inserts on the cnemial crest via a tendon with femorotibialis
externus.
• FMTI attaches to the femur and envelops the dorso-lateral portion of this
bone.
• It is involved in knee extension.
• Femorotibialis externus (FMTE)
• This muscle originates by a fleshy attachment approximately one third of
the way down the dorsal femur.
MAGEJA.T@VETHACKING.COM.REVISION NOTES
Hindlimb muscles
• It inserts on the proximo-lateral cnemial crest by a small tendon.
• FMTE merges with femorotibialis internus by a tendon at its insertion
point but is separated at origin by the iliofemoralis.
• It lies posterior to femorotibialis internus and is smaller than this
muscle.
• It functions as a knee extensor.
• Deep ventral muscles of the upper hindlimb.
• Caudofemoralis longus (CFL) (coccygeo- femoralis longus ; caudi-
femoralis

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Fig 15. Deep dorsal muscles of the upper hindlimb. FMTE: Femorotibialis externus, IF: Iliofemoralis,
FMTI: Femorotibialis internus. MAGEJA.T@VETHACKING.COM.REVISION NOTES
Fig 16. Deep ventral muscles of the upper hindlimb. CFL: Caudofemoralis longus, CFB: Caudofemoralis
brevis, PIFI1-2: Pubo-ischio-femoralis internus 1-2, ADD 1-2: Adductor 1-2, PIFE 2-3: Pubo-ischiofemoralis
externus 2-3. MAGEJA.T@VETHACKING.COM.REVISION NOTES
Hindlimb muscles
• This muscle originates by a fleshy attachment in the tail at numerous
caudal vertebral haemal arches beginning at caudal vertebra 12.
• It inserts via a very large tendon on the proximoventral femur at the
fourth trochanter.
• This muscle also has an accessory tendon that attaches at the ventro-
distal femur on the tibial condyle with the gastrocnemius externus.
• This accessory tendon is covered in dorsal view by iliotibialis 3 and
flexor tibialis externus.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Hindlimb muscles
• The proximal third of this muscle, between its origin and insertion
points, sits free from the caudal vertebrae and is therefore
constrained by the hypaxial musculature, namely the transverse
perenei, and also a layer of fat that separates the CFL from the
hypaxial muscles.
• CFL is the largest muscle in the crocodile's body and performs the
majority of the hip extension along with caudofemoralis brevis.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Hindlimb muscles
• Caudofemoralis brevis (CFB) (coccygeo-femoralis brevis ; caudi-
femoralis )
• This muscle originates in the tail by two heads, one from the postero-
lateral ilium and the other to caudal vertebrae 4 and 5, anterior to the
origin of caudofemoralis longus.
• It inserts by a tendon at the proximo-ventral femur on the fourth
trochanter.
• It lies antero-medial to the caudofemoralis longus and is the smaller
of the two major hip extensors.
• Adductor (ADD) (adductor femoris ; ischio-femoralis )

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Hindlimb muscles
• This muscle is composed of 2 parts.
• ADD1 originates by a fleshy attachment at the ventrolateral surface of
the ischium and inserts via a tendon at the at the ventro-medial
femur.
• ADD2 lies posterior to ADD1.
• It also originates by a fleshy attachment on the ventro-lateral ischium
and inserts on the disto-ventral femur again by a fleshy attachment. It
is much longer and thinner than ADD1.
• The adductor is important for hip adduction and also contributes to
extension of the hip joint.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Hindlimb muscles
• Pubo-ischio-femoralis externus (PIFE)
• This muscle is composed of 3 parts. PIFE1 originates on the anterior
boarder of the pubis, anterior to PIFE2, by a fleshy attachment.
• It inserts on the proximo-anterior femur with the other two parts of
PIFE.
• PIFE2 originates from the entire lateral pubis and inserts via a tendon
at the proximo-anterior femur.
• It is a fan-shaped muscle. PIFE3 originates by a fleshy attachment on
the antero-lateral margin of the ventral ischium and inserts by a
tendon on the proximo-anterior femur with PIFE2.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Hindlimb muscles
• It is less broad than PIFE2 but is thicker. PIFE functions as a hip
adductor and also function as a hip adductor.
• Pubo-ischio-femoralis internus (PIFI) (quadratus lumborum)
• This muscle is composed of 2 parts.
• PIFI1 originates on the medial ilium and proximomedial ischium by a
fleshy attachment, and inserts on the proximal femur, medial to the
fourth trochanter and between the insertion of pubo-ischio-femoralis
externus 3 and adductor 1.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Hindlimb muscles
• It is a short but thick muscle.
• PIFI2 originates anterior to the pelvic girdle by a fleshy attachment on
the transverse processes of the few vertebrae anterior to the girdle.
• It inserts by a tendon onto the proximo-lateral femur near the fourth
trochanter.
• It is a fan-shaped muscle.
• PIFI1 acts as a hip adductor while PIFI2 acts to both abduct and flex
the hip.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Hindlimb muscles
• It also function as a hip adductor function, as in PIFI1, rather than
abduction .
• Superficial dorsal muscles of the lower hindlimb.
• Gastrocnemius externus (GE)
• This muscle originates by a fleshy attachment at the caudofemoralis
longus tendon on the postero-distal femur.
• It inserts by a wide tendon onto the lateral calcaneus.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Hindlimb muscles
• It is a sizeable muscle, making up a large portion of the postero-lateral
lower limb.
• It is largely responsible for extension of the knee.
• Tibialis anterior (TA) (tibialis anticus)
• This muscle originates via a fleshy attachment on the antero-proximal
tibia.
• Insertion is by a tendon into the dorsal surface of digits 2 and 3.
• It is a large and elongate muscle covering the anterior tibia and is
involved in ankle flexion.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Hindlimb muscles
• Fibularis longus (FL)
• This muscle's origin is on the proximo-medial tibia by a tendon and it
inserts by a tendon at the astragalus.
• The FL lies postero-medial to tibialis anterior.
• It acts to flex the ankle.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
 Fig 17. Superficial dorsal muscles of the lower
hindlimb. GE:Gastrocnemius externus, TA:
Tibialis anterior, FL: Fibularis longus.
MAGEJA.T@VETHACKING.COM.REVISION NOTES
 Fig 18. Superficial ventral
muscles of the lower
hindlimb. GI: Gastrocnemius
internus, EDL: Extensor
digitorum longus, EDB:
Extensor digitorum brevis.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Hindlimb muscles
• Superficial ventral muscles of the lower hindlimb .
• Extensor digitorum longus (EDL) (extensor digiti )
• This muscle originates as a narrow tendon on the lateral fibula, and
inserts onto the dorsal surface of the digits via a tendinous
attachment.
• It lies postero-lateral to tibialis anterior.
• The EDL is involved in ankle extension.
• It also functions as a digit extensor.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Hindlimb muscles
• Extensor digitorum brevis (EDB) (peroneus posterior )
• This muscle originates by a fleshy attachment at the latero-distal fibula and
inserts into the dorsal pes at digit 5.
• It is a small but broad muscle and lies distal and posterior to the extensor
digitorum longus and fibularis brevis.
• EDB functions to extend the pes.
• Gastrocnemius internus (GI)
• This muscle originates by a tendon from the proximo-medial tibia and
inserts at the ventral calcaneus by a tendon with the gastrocnemius
externus.
• It is wide but thin and lies deep to the gastrocnemius externus. GI is one of
the ankle extensors.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
 Fig 19. Deep dorsal muscles of the lower
hindlimb. FDL: Flexor digitorum longus,
FHL: Flexor hallucis
longus, PP: Pronator profundus.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Hindlimb muscles
• Deep dorsal muscles of the lower hindlimb.
• Flexor digitorum longus (FDL)
• This muscle originates by a tendon on the ventro-lateral femur at the
lateral condyle and inserts into the ventral pes by a tendon.
• This muscle is long and wide but quite thin.
• It lies directly over the flexor hallucis longus and is a knee extensor and
also a digit flexor.
• Flexor hallucis longus (FHL) (tibialis posticus )
• This muscle originates by a fleshy attachment from the lateral condyle of
the femur and inserts by a tendon past the knee and into the ventral pes.
• It is wide at the proximal end and tapers towards insertion.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Hindlimb muscles
• It covers much of the postero-ventral fibula and functions to extend
the knee and flex the digits.
• Pronator profundus (PP)
• This muscle originates from the disto-lateral fibula via a fleshy
attachment.
• It inserts at the tarsals, again by a fleshy attachment. PP is a small
and almost spherical muscle on the disto-lateral fibula.
• It is involved in ankle extension, while its ability to pronate the ankle
seems to be limited by its small size.
• Deep ventral muscles of the lower hindlimb.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Hindlimb muscles
• Fibularis brevis (FB) (peroneus anterior )
• This muscle originates on the lateral fibula by a fleshy attachment and
inserts via a tendon on the dorsal surface of metatarsal 3.
• This muscle is narrow at origin but broadens towards insertion before
becoming tendinous.
• It lies posterior to extensor digitorum longus.
• It functions to flex the ankle joint.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Hindlimb muscles
• Interosseus cruris (IC)
• This muscle originates by a tendon at the proximo-medial tibia and
fibula.
• It inserts via a tendon into the ventral pes.
• It lies between the tibia and fibula and fills the space between these
two bones.
• It functions to assist in ankle joint flexion.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Fig 20. Deep ventral muscles of the lower hindlimb. FB:
MAGEJA.T@VETHACKING.COM.REVISION NOTES
Fibularis brevis, IC: Interosseus cruris.
Skeletal system
• The crocodilian skeleton is typical of that of tetrapods in general and of
archosaurs in particular, with the skull and pelvis particularly specialised
• Also of interest are the structure of the head vertebrae (atlas and axis), the
osteoderms, and the gastralia, or stomach ribs, which protect the ventral
surface.
• As archosaurs, crocodilians are diapsid, although the post-temporal
fenestrae are reduced.
• Palatal and external mandibular fenestrae and ossified laterosphenoids are
present.
• The wall of the braincase is ossified, but supratemporals and postfrontals
are absent.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Skeletal system
• The pterygoid and quadrate adhere tightly to the lateral wall of the
braincase and the otic notch closes posteriorly.
• All species lack a parietal (pineal) foramen.
• The premaxillae are expanded postero-dorsally, isolating the external
nares from the maxillae.
• Internal nares are prolonged posteriorly by a secondary palate formed
of the palatal processes of the premaxillae, maxillae, palatines and
pterygoids and the secondary choanae open within the pterygoids

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Skeletal system
• The premaxilla, maxilla and dentary bear peg-like conical thecodont
teeth
• The largest teeth of the upper jaw are premaxillary 4 in the
Alligatoridae, premaxillary 5 in the Crocodylidae, and maxillary 9 and
11 and dentary 1, 4, 11 and 12 throughout this group.
• The vertically undulating jawline coincides with the distribution of
the largest teeth, thus accentuating the pseudoheterodonty,
particularly in the shorter-snouted species.
• In the long snouted, fish-eating crocodilians, the teeth are more
uniform in size, approaching a homodont condition, and the jawline is
straight rather than undulating
MAGEJA.T@VETHACKING.COM.REVISION NOTES
Skeletal system
• The premaxilla, maxilla and dentary bear peg-like conical thecodont
teeth
• The largest teeth of the upper jaw are premaxillary 4 in the
Alligatoridae, premaxillary 5 in the Crocodylidae, and maxillary 9 and
11 and dentary 1, 4, 11 and 12 throughout this group.
• The vertically undulating jawline coincides with the distribution of
the largest teeth, thus accentuating the pseudoheterodonty,
particularly in the shorter-snouted species.
• In the long snouted, fish-eating crocodilians, the teeth are more
uniform in size, approaching a homodont condition, and the jawline is
straight rather than undulating
MAGEJA.T@VETHACKING.COM.REVISION NOTES
Skeletal system
• In the Alligatoridae, the 4th dentary tooth fits into a pit in the upper
jaw at the junction of premaxilla and maxilla, and the mandibular
tooth rows lie inside the upper tooth rows at occlusion.
• In the Crocodylidae and Gavialidae, upper and lower teeth alternate
at occlusion, and the 4th dentary tooth fits into a lateral notch at or
near the junction of the pre-maxilla with the maxilla.
• Thus the teeth of crocodiles are far more conspicuous than those of
alligators when the mouth is closed.
•

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Skeletal system
• Teeth generally are replaced continuously with new ones
growing from below in the same socket, but this process
slows down and stops in older individuals; some of the
largest individuals are likely to be edentulous.
• Cranial sculpturing becomes more complex with age as a
result of secondary dermal ossifications on the dorsal
surface.
• Some (Osteolaemus species and Palaeosuchus palpebrosus)
have palpebral osteoderms in the upper eyelids.
MAGEJA.T@VETHACKING.COM.REVISION NOTES
Skeletal system
• The middle ear region is modified extensively, and the quadrate is inclined
so that the hinge of the jaw is displaced far posteriorly.
• Cranial growth is allometric and the naris-eye dimension increases several
times faster than that between eye and condyle.
• As the olfactory bulbs lie close to the nares, the proportions of the brain
reflect those of the skull.
• Many cranial bones are pneumatised, and have gas-filled cavities
connected to the Eustachian tubes of the middle ear and the nasal
passages.
• These may equalise pressure in the inner ear , or isolate the inner ear from
underwater sounds when listening above water

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Skeletal system
• However, pneumatisation also reduces the cranial mass (and inertia),
while maintaining its strength, which is an important consideration in
both buoyancy and feeding.
• The nine cervical vertebrae are keeled ventrally.
• The last two to five of the 15 to 16 dorsal vertebrae lack free ribs.
• The caudal vertebrae bear relatively long neural and haemal spines,
as well as chevron bones on the anterior two-thirds.
• The cervical ribs are solid and the dorsal ones articulate ventrally with
two partly calcified elements, the ventral-most of which reaches the
sternal system.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Skeletal system
• The most superficial gastralia are located between the sternal region
and the pelvic girdle.
• The shoulder girdle is simple and plate-like, and the three
components of the pelvic girdle radiate from the articular fossa.
• The Nile crocodile has 11 to 13 thoracic ribs and six to seven
abdominal ribs.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
MAGEJA.T@VETHACKING.COM.REVISION NOTES
MAGEJA.T@VETHACKING.COM.REVISION NOTES
MAGEJA.T@VETHACKING.COM.REVISION NOTES
MAGEJA.T@VETHACKING.COM.REVISION NOTES
Locomotion and buoyancy
• Crocodilians are amphibious, but travel most easily in water which they
traverse with sinuous movements of the strong, laterally compressed tail,
holding the limbs at the sides.
• On land they have several gaits: walking, high walking with the body held
clear of the ground, running and, in some species, a galloping gait in which
limbs of the two sides move in unison, driven by dorsoventral flexion of the
vertebral column.
• They also undulate down steep slopes.
• Galloping is a conspicuous escape movement in C. johnstoni
• Although they can travel at great speed, such bursts are short lived as they
are sustained by anaerobic metabolism.
• Crocodiles can travel substantial distances both overland and by sea

MAGEJA.T@VETHACKING.COM.REVISION NOTES
MAGEJA.T@VETHACKING.COM.REVISION NOTES
Locomotion and buoyancy
• Crocodilians manage their buoyancy very skilfully.
• They are denser than water and achieve neutral buoyancy by
appropriate inflation of the lungs.
• Shallowly breathing crocodilians are able to float at the water surface
for long periods, the water line constant within a couple of
millimetres just below the eye
• It is unlikely that pulmonary volume can be modified by muscular
contraction during a dive, but negative buoyancy increases with
depth as the lungs are compressed and as oxygen is removed and
replaced with a smaller volume of carbon dioxide.
MAGEJA.T@VETHACKING.COM.REVISION NOTES
Locomotion and buoyancy
• Most larger crocodilians accumulate gastroliths (stomach stones),
including individuals which live in areas where stones are uncommon,
implying that some effort may be made to collect them.
• Larger crocodiles have a larger burden of stones
• The gastroliths do not increase specific gravity, because the crocodiles
compensate for added load by inhaling more deeply.
• The stones may function as a counterpoise for the weight of the head,
which increases proportionally with increasing age.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Digestive system
• Crocodilians are carnivorous, sit-and-wait predators, which rely on
swift attack from the water to seize large terrestrial prey and
immobilise it before it is swallowed.
• Smaller prey is commonly taken by a sideways strike of the head,
which reduces the change of cranial momentum.
• It may then be broken up by being lifted from the water and
‘whiplashed’, in a similar manner to that used by monitor lizards.
• Large prey may be stored until it starts to disintegrate.
• In cooperative feeding, several individuals grasp a single prey item
and dismember it by twisting in opposite directions.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Digestive system
• The hard palate and the palatal flap at the back of the buccal cavity
allow food to be held in the mouth for long periods without
interrupting the respiratory flow, while prey is dismembered or
drowned.
• Food is commonly picked up near the anterior tips of the jaws.
• It is repositioned and shifted toward the oesophagus, by inertial
feeding , in which the jaws quickly release and shift the food to a new
position before it can fall far.
• More effective in air than in water and, in addition to breathing, may
explain why ingestion usually occurs with the head above the water.
MAGEJA.T@VETHACKING.COM.REVISION NOTES
Digestive system-oral cavity
• The oral cavity had the form of an isosceles triangle and is dorso-
ventrally flattened, severely limiting the space within the cavity.
• The roof of the cavity is formed exclusively by the palate and the
indistinct gingiva with which it is continuous.
• The caudal limit of the roof was demarcated by the notched dorsal
component of the gular valve, whereas the rostral limit of the palate
is occasionally characterised by the presence of two deep pits which
accommodated the first two incisors of the mandible

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Digestive system-oral cavity
• Between the two pits (or at the base of the two I 1 teeth) is a small,
rigid, conical process which emerged from a low-profiled ridge above
the anterior palatine foramen.
• The tip of this process is housed within a shallow depression in the
mandible at the base of the first two mandibular incisors.
• The floor of the oral cavity is formed by the tongue and a wide, rostral
mucosal plate continuous with the gingiva.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Digestive system-oral cavity
• The relatively long non-protrusible tongue is roughly triangular in
shape, being much broader caudally than at its tip with lingual
papillae covering the dorsal surface from the root to the tip.
• It occupies the greater part of the floor of the oral cavity (apart from
the rostral plate over the symphysis of the dentary bones) and is
bordered peripherally by a loose, highly folded, continuous, fibrous
membrane
• Practically no function in the ingestion of food, being devoid of
gustatory buds.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
MAGEJA.T@VETHACKING.COM.REVISION NOTES
Macrophotograph of the mandible with the tongue in situ showing the dental arrangement
of the incisor (I 1–3), canine (C 1–5) and molar (M 1–7) teeth, demarcated by the stippled
lines. The sampling sites for histology of the gingivae (D and E) are also indicated. The
rostral dentary shelf is indicated in the region above the symphysis of the dentary bones.
The black arrowhead indicates the position of the shallow depression which houses the
small, rigid, conically formed process,situated at the base of the I 1 teeth, seen in Fig. 2. The
glottis (GT) and laryngeal mound (LM) are shown in situ on the floor of the pharyngeal
cavity and the ventral fold (VF) of the gular valve is seen separating the ventral aspects of
the oral and pharyngeal cavities.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Digestive system
• The crocodilian gut is comparatively short and simple and the viscera are
typically reptilian
• The gastrointestinal tract of crocodiles is composed of a mouth, esophagus,
stomach, small intestine and large intestine without a cecum
• Chunks of food are swallowed whole and pass to the stomach via a long
oesophagus.
• The stomach lies posterior to the heart, which is positioned about midway
between the front and rear limbs.
• The cardiac sphincter occurs at the junction of the oesophagus with the
cardiac sac at the left anterior corner of the stomach.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Digestive system
• The esophagus is a straight tubular organ located caudally to the short
pharynx, dorsally to the trachea, passing between the main bronchi of the
trachea and the right and left lungs, and ending cranially in the stomach
along the median line.
• The esophageal wall of the species examined in this study appears to be
predominantly muscular, indicating a similarity to studies on Alligator
mississippiensis, which apply to the other crocodilians and mammals, but
differing from the latter by its greater thickness
• Internally, the wall shows creases arranged longitudinally, which
sometimes bifurcate or converge.
• The middle third of the esophagus is clearly dilated and its wall is thinner
due to the passage of large food items ingested by crocodilians, as reported
by Santos.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
 Fig. 1. Digestive system of
specimens of C. crocodilus, P.
palpebrosus and M. Niger
from the LAPAS collection.
Ventral
views. A – C. crocodilus: TO,
tongue; PH, pharynx; TR,
trachea; ES, esophagus; RL,
right lung; LL, left lung; LPB,
left
primary bronchus; RLL, right
lobe of liver; LLL, left lobe of
liver; ST, stomach; SI, small
intestine; LI, large intestine;
CL,
cloaca. B – P. palpebrosus. PH,
pharynx; ST, stomach; SP,
spleen; DU, duodenum; JE,
jejunum; IL, ileum; LI, large
intestine; CL, cloaca. C – M.
Niger.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Digestive system
• The longitudinal creases in the proximities of the gastroesophageal
transition zone broaden and become less numerous, and the region
becomes more constricted

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Digestive system
• The cardiac sac is divided into left and right halves by a thick collar of
muscle and spongy tissue, which may operate as a gizzard.
• The pyloric region is much smaller, and opens to the duodenum via a
pyloric sphincter
• It is likely that the cardiac (or fundic) stomach has a glandular epithelium
which secretes HCl and pepsinogen,whereas the pyloric portion secretes
mucus.
• As crocodilians do not secrete chitinases, chitinous and keratinous remains,
snail opercula and fur accumulate in crocodilian gut contents.
• Such indigestible remnants are likely to be cast out via the mouth, as in
many avian species.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Digestive system
• The main portion of the stomach is located in the left antimere in a
horizontal circumvallated projection, and not immediately in the
aforementioned antimere in an elongated and longitudinal projection, as in
Hemidactylus mabouia.
• Located between the esophagus and the duodenum, it represents the most
dilated part of the gastrointestinal tract is the principal site of digestion in
crocodilians and is functionally similar to the muscular stomach, or gizzard,
of birds.
• It has a large chamber with ventral and dorsal walls of the same thickness,
differing from the description given by Wallach (1971), who stated that the
stomach of Caiman yacare is divided into two distinct chambers, a thick-
walled anterior one and a thin-walled posterior one, without specifying an
intermediary delimitation.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Digestive system
• Four distinct gastric regions are visible: the cardia (small, and
corresponding to the cranial end of the stomach, sequent to the
gastroesophageal transition zone), the fundus (to the left of the
cardiac region, forming a conspicuous cranial angle), the corpus (the
region with the largest diameter and length), and the pyloric chamber
(the terminal region of the stomach, which ends in the pyloric
sphincter)
• The cardiac region may be large or small, and that the convoluted
longitudinal creases found in the stomach lumen – except in the
pyloric region due to the greater constriction at its terminal end –
may or may not be present,

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Digestive system
• The stomach of Hemidactylus mabouia can be divided into an oral
fundic, an aboral fundic and a pyloric region, while the stomach of
other crocodilians is divided the into a fundic and a pyloric region.
• In the gastroduodenal transition zone the pyloric sphincter is visibly
constricted allowing for passage to the duodenum only of liquid or
pasty food that has already been neutralized by mucous glands in the
pyloric region.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Digestive system
• Crocodilians digest flesh and bones fully, including that from fresh
carcasses, and cache only very large prey for its initial dismemberment.
• Concerning control mechanisms, gastrin/ cholecystekinin-like hormones
are secreted by the pyloric mucosa, and emphasise the similarity of
Crocodylia to other vertebrates
• The stomach is situated to the left of the abdominal cavity, between the
tenth thoracic and the sixth abdominal ribs, with the greater curvature
facing to the left
• A very acute angle is present between the cardia and pylorus
• An oval to round, dorso-ventrally flattened, encapsulated portion of
adipose tissue, the so-called "fat body", occupies the right cranial part of
the abdominal cavity

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Digestive system
• Starting from the pyloric sphincter, the small intestine coils through the
medial and caudal segments of the coelomic cavity, ending in the large
intestine.
• The small intestine is divided into three segments: the duodenum, jejunum
and ileum, which are continuous and devoid of a macroscopic delimitation.
• These segments are identified through topographical inferences and their
progressively diminishing villosity.
• The duodenum begins in the right antimere lateral to the stomach.
• Its diameter decreases progressively along its length, with a winding
projection constricted at some levels, lodging the pancreas between two
well defined loops that touch the liver directly and that begin after a short
transverse projection,

MAGEJA.T@VETHACKING.COM.REVISION NOTES
 Fig. 2. Digestive system of a P.
palpebrosus specimen from the
LAPAS
collection. Dorsal views. RLL, right
lobe of liver; LLL, left lobe of liver;
CO, direct connection of the liver to
the pancreas; BDp; biliary duct
emptying into the pancreas; GBl,
gallbladder duct emptying into the
liver;
PA, pancreas; GB, gall bladder; ST,
stomach; DU, duodenum; JE,
jejunum;
SP, spleen.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Digestive system
• The wall of the small intestine is visibly thicker in the duodenum,
presenting several villosities in its internal anatomy, which indicate
greater adsorption capacity.
• These villi decrease progressively toward the caudal portion of the
ileum
• The diameter of the large intestine is about three times larger than
that of the small intestine, with a dilated wall tending toward
• collapsibility.
• The large intestine is separated from the small intestine by a
sphincter

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Digestive system
• The cloaca is located at the shared end of the digestive, urinary and
genital systems.
• The longitudinal creases extending along its inner wall ensure
considerable distension capacity

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Digestive system
• The duodenum is arranged in the form of a double loop on the right, with
the pancreas situated between the arms of the outer loop.
• The pancreas also extends to the cranial broad part of the spleen and along
the proximal part of the jejunum.
• The latter part is attached to the dorsal body wall.
• The ileum and jejunum, which are of equal length, fill the right and left side
of the peritoneal cavity.
• The proximal part of the jejunum is firmly attached to the dorsal body wall.
• The mesentery then lengthens to allow free coiling of the remaining
portions of the jejunum and ileum.
• The rectum (in the midline) extends into the cloaca
MAGEJA.T@VETHACKING.COM.REVISION NOTES
Digestive system
• The liver, which consists of right and left lobes, is situated in its own
coelomic cavity, the hepatic coelom,which is bound cranially by the
post-pulmonary membrane and caudally by the post-hepatic
membrane.
• These two membranes are intimately associated with the cranial and
caudal surfaces of the liver, respectively.
• The right and left pleural cavities communicate with the hepatic
coelom by means of two openings situated left and right dorsally in
the membranous part of the post-pulmonary membrane.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Digestive system
• The liver, bilobed and with a conical shape, is located cranially in the
coelomic cavity.
• The right lobe is larger than the left lobe, the former touching the gall
bladder and the first two loops of the duodenum and the latter
touching the cranial surface of the stomach.
• The medial dorsal and caudal region of the right lobe contains the
hepatic hilum and a piriform gall bladder, which receives a hepatic
duct and sends out another duct to the pancreas, as well as a
connection linked directly to the pancreas, which bifurcates close to
the hilum.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Digestive system
• The empty gallbladder has a flattened sac-like shape and is attached
caudally to the dorso-medial aspect of the right liver lobe by the
hepatocystic ligament.
• When fully distended the gallbladder has the form of a blind-ending
pouch with its body lodged ventromedially between the duodenum
on the right and the stomach on the left

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Digestive system
• It should be noted that these ducts precede the pancreatic ducts,
which in turn unite to form the hepatopancreatic ampulla, perforating
the duodenum through the duodenal papilla.
• The biliary ducts responsible for draining bile from the hepatic lobes
unite to form the main right and left ducts, which, together with the
cystic duct, form the choledoc duct that opens into the initial portion
of the duodenum.
• The pancreas is lodged between the first two dorsal duodenal loops,
one ascending cranially and the other descending caudally, projecting
immediately after the first lateral flexure to the right of the pyloric
region is from the pylorus, as in Pseudemys scripta .

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Digestive system
• The pancreas extends dorsally without touching the spleen directly at
its terminal segment, since the latter is attached to the medial edge
of the descending duodenal flexure, differing from the description of
Alligator mississippiensis in the direct final connection to the spleen.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Digestive system
• The dissection of the gastro-intestinal tract revealed the stomach of
which the minor curvature displayed a very acute angle, resulting in
the cardia and pylorus lying adjacent to each other.
• A pyloric antrum or dilatation is separated from the main part of the
stomach by a distinct sphincter.
• The duodenum is arranged in a double U-shaped loop with the
proximal part of the duodenum forming the inner loop and the distal
part the outer loop.
• The jejunum is situated between the duodenum and ileum.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Digestive system
• The beginning of the latter is demarcated by the presence of the A.
mesenterica cranialis.
• An ileorectal junction is present where the narrow ileum abruptly
changes into the wide rectum .
• The rectum continues into the cloaca

MAGEJA.T@VETHACKING.COM.REVISION NOTES
MAGEJA.T@VETHACKING.COM.REVISION NOTES
MAGEJA.T@VETHACKING.COM.REVISION NOTES
MAGEJA.T@VETHACKING.COM.REVISION NOTES
MAGEJA.T@VETHACKING.COM.REVISION NOTES
Respiratory system
• In the Crocodilia the framework of the larynx consists of three
cartilages, of which two represent the arytenoids of the Mammalia;
the third represents the thyroid and cricoid of mammals.
• The last is considerably larger than the first and is a broad closed ring,
differing in form in the different species.
• The vocal apparatus is produced by the projection into the laryngeal
cavity of the inner border of the small arytenoid cartilages and by the
infolding, under these cartilages, of the mucous membrane of the
larynx; this forms the thick but fairly free folds that, when the glottis
is narrowed, are well adapted to produce the harsh tone of the
animal.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Respiratory system
• The epiglottis is absent in the Crocodilia.
• At the thoracic inlet the trachea is situated to the left of the
oesophagus which lies in the midline within the dorsal mesentery.
• The trachea then turns abruptly to the right before dividing into a left
and right primary bronchus
• In many Crocodilia the trachea forms a loop
• It is a short vertical partition in the stem just before its division into
the two branches.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Respiratory system
• This partition is partly membranous and possesses one or more stiffening
cartilaginous strands which are outgrowths of so many cartilaginous rings of the
trachea.
• Most of the tracheal rings are closed, but a varying, though at most small,
number are open on the dorsal side.
• These openings become wider as the larynx approach the lungs
• The lungs, together with the heart (including pericardium and the great vessels)
and the oesophagus occupy the cranial half of the body cavity.
• The pleural cavity is divided into separate left and right cavities by means of a
complete mediastinum.
• The cavities are roughly triangular in shape, with the base situated caudally and
the apex terminating in cupulae, both extending a short distance (± 15 mm)
beyond the first thoracic rib.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Respiratory system
• Caudally, the pleural cavity is bound by a post-pulmonary membrane
and divided into left and right cavities by means of a complete
mediastinum.
• The diaphragmatic surfaces of the two lungs are attached to the post-
pulmonary membranes, while the caudal third of the medial borders
are attached to the mediastinum.
• Each lung lies in a separate, closed pleural space, bordered laterally
by the dorsal ribs and intercostal musculature, dorsally by the
vertebral column, medially by the mediastinum, and ventrally by the
sternal ribs.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Respiratory system
• The lungs, particularly in the dorsal half, tend to fuse with the parietal
pleural surface.
• Right and left lungs are mirror images of each other reflected in the
mediosagittal body plane.
• Each represents approximately a truncated cone, with its base lying against
the liver and its cranial apex extending ventrally into the base of the neck,
between the shoulder girdle and the oesophagus.
• The lungs are multicameral, consisting of a variable number of chambers
(camera), each of which connects independently with an unbranched,
intrapulmonary bronchus
• The cranial half of the intrapulmonary bronchus is cartilage reinforced.
• It displays three rows of orifices which supply four dorsal chambers, four
lateral chambers and three ventral chambers
MAGEJA.T@VETHACKING.COM.REVISION NOTES
Respiratory system
• The paired lungs are well developed and well perfused, and lie in the
thorax, served by a trachea which originates anteriorly in a glottis which
can be closed.
• The latter lies on the floor of the posterior pharyngeal cavity and is
supported by the cartilaginous hyoid plate.
• Interestingly, in large C. porosus and perhaps in other species, the trachea
forms a large loop in the upper thorax, reminiscent of a water-trap, but its
function is unknown
• The Nile crocodile has 11 to 13 thoracic ribs and six to seven abdominal
ribs.
• At the thoracic inlet the trachea is situated to the left of the oesophagus
which lies in the midline within the dorsal mesentery.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Respiratory system
• The trachea then turns abruptly to the right before dividing into a left
and right primary bronchus.
• The pleural cavity is divided into separate left and right cavities by
means of a complete mediastinum.
• The cavities are roughly triangular in shape, with the base situated
caudally and the apex terminating in cupulae, both extending a short
distance beyond the first thoracic rib

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Respiratory system
• Caudally, the pleural cavity is bound by a post-pulmonary membrane and
divided into left and right cavities by means of a complete mediastinum.
• The diaphragmatic surfaces of the two lungs are attached to the post-
pulmonary membranes, while the caudal third of the medial borders are
attached to the mediastinum
• During ventilation the glottis is lifted into close proximity to the internal
nares, and the gases then pass above the secondary palate to and from the
exterior via the external nares.
• The palatal flap at the rear of the buccal cavity prevents the entry of water
into the posterior pharynx, even when the open mouth holds prey.
• During swallowing, the glottis is closed and depressed, and the palatal flap
opened.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Respiratory system
• In crocodilians, the liver is connected to the body wall by an annulate
connective tissue sheet which divides the pleural and visceral cavities.
• Inspiration is effected by contraction of portions of the intercostal
muscles which distend the rib cage, and of the m. diaphragmaticus
which retracts the liver caudally.
• Expiration is by contraction of the superficial intercostal muscles, and
of the transverse abdominal muscles which move the liver forward,
thereby decreasing the pleural volume.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Figure 40.5 Respiration in Crocodylus porosus. A, expiration; B, inspiration.
lng, lungs; liv, liver; mat, m. abdominalis transversus; mdp,
MAGEJA.T@VETHACKING.COM.REVISION NOTES
m. diaphragmaticus; mis, m. intercostalis superficialis. [D. Kirshner]
Respiratory system
• Apart from their importance as an oxygen store and a carbon dioxide sink,
crocodilian lungs are important in controlling buoyancy.
• Indeed, the volume of the lungs in a swimming or diving individual is
determined by buoyancy requirements, not oxygen store demands
• The lungs are multicameral, consisting of a variable number of chambers
(camera), each of which connects independently with an unbranched,
intrapulmonary bronchus .
• The cranial half of the intrapulmonary bronchus is cartilage reinforced.
• It displays three rows of orifices which supply four dorsal chambers, four
lateral chambers and three ventral chambers.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Respiratory system
• A medial row is lacking.
• The rows of orifices do not run parallel to the long axis of the
intrapulmonary bronchus, but instead form a left hand spiral in the
left lung (right-hand in the right lung).
• Hence the first lateral chamber opens into the lateral aspect of the
intrapulmonary bronchus, but the orifice of the fourth lateral
chamber is dorsal
• The first dorsal chamber is rudimentary. The remaining chambers in
the dorsal row are long, tubular structures.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Respiratory system
• Together with a cluster of medial chambers which originate at the end of
the cartilage-reinforced portion of the intrapulmonary bronchus, they form
a dorsomedial lung lobe.
• The cavernous first lateral chamber extends cranially from its bronchial
entrance and, together with its large ventral and lateral branches, forms
the lung apex
• Lateral chambers 2-4 make up the deep lateral and superficial dorsal
portions of the lung along the middle third of its length.
• In the middle third of the lung the three ventral chambers comprise the
sac-like ventrolateral and ventromedial lung regions.
• The first two ventral chambers then double back dorsally and form the
superficial lateral portion of the lung

MAGEJA.T@VETHACKING.COM.REVISION NOTES
 Fig. 1. Semi-schematic representation of the left lung of
Crocodylus niloticus in lateral
view (A) and medial view (B), showing the distribution of
chambers. Chambers
onginating in the cartilage-reinforced portion of the
intrapulmonary bronchus (outlined
by solid lines) occur in spiralling rows and are indicated:
dorsal row, D1-D4; lateral row,
L1-L4; ventral row, V1-V3. In the cartilage-free portion of the
intrapulmonary
bronchus only the major, tubular chambers are indicated by
letters, indicating their
dorsal (D' and D"), ventral (V and V") or lateral (L') origin. At
the transition between
the two portions of the intrapulmonary bronchus a cluster of
four medial chambers
(M1-M4) originates. Other, smaller chambers are numerous
and irregular in occurrence.
The intrapulmonary bronchus ends in a terminal chamber (T).
The drawing is based
upon the dissection of dried specimens from two C. niloticus
and upon comparison with
similar preparations from C. porosus and Caiman crocoddus.
The right lungNOTES
MAGEJA.T@VETHACKING.COM.REVISION does not
differ substantially from a mirror image of the left.
Respiratory system
• The caudal half of the intrapulmonary bronchus lacks cartilage and its chambers
are not continuous with the rows described above.
• In addition to the cluster of medial chambers mentioned above, five long, tubular
chambers and the sac-like terminal chamber supply the superficial portions,
while a large number of irregularly distributed outgrowths (bronchial niches)
supply the deep lung parts.
• The inner surface of the chambers is elaborated with a system of cubicles
(ediculae).
• The free edges of the ediculae face the central lumen of the chambers and are
supported by a system of stout trabeculae, as described for amphibian and
reptilian lungs
• The interedicular septa, which bear the respiratory capillaries, are often
perforated, whereas the intercameral septa, which separate adjacent chambers,
rarely show such perforations.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
MAGEJA.T@VETHACKING.COM.REVISION NOTES
Fig. 15. Diagrammatic images in dorsal view of (A) the pulmonary
arteries and (B) pulmonary veins that are based on conventional pulmonary
arteriography and CT scan 3D reconstructions. Shaded vessels
in (A) are more ventrally positioned. A semitransparent 3D
airspace reconstruction stereo pair (C,D) and 3D surface volume rendering
with dorsal cut away (E) are included to illustrate the challenges
of interpreting the anatomy in three dimensions. Abbreviations: CVL—
cranioventral lateral branch (br), CVM—cranioventral medial br.,
DCrT—dorsal br. cranial trunk (tr.), DLcaCaT—dorsolateral caudal br.
caudal tr., DLcrCaT—dorsolateral cranial br. caudal tr., DLCrT—dorsolateral
br. cranial tr., DMcaCaT—dorsomedial caudal br. caudal tr.,
DMcaCrT—dorsomedial caudal br. cranial tr., DMcrCaT—dorsomedial
cranial br. caudal tr., DMCrT—dorsomedial br. cranial tr., DMcrCrT—
dorsomedial cranial br. cranial tr., LCaT—lateral br. caudal tr.,
VMCaT—ventromedial caudal tr., VMCrT—ventromedial cranial tr.,
VMP—ventromedial pericardial br.
MAGEJA.T@VETHACKING.COM.REVISION NOTES
Cardiovascular system
• The crocodilian heart is most sophisticated
• Combines features of both mammalian ,avian as well as other
reptilian hearts
• Unlike other reptiles, crocodilians have a complete four chambered
heart with two atria and two ventricles.
• Structure and pressure balance are similar to those of birds and
mammals, with a high pressure (60 to 100 mm Hg) systemic circuit
and a low pressure (15 to 20 mm Hg) pulmonary circuit.
• the system also incorporates a number of
• unusual features which endow strong pulmonary bypass capabilities.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Cardiovascular system
• Firstly, the left systemic arch persists as a small vessel which leaves from
the right ventricle, alongside the pulmonary arch! It runs dorso-laterally
above the lungs to join the dorsal aorta (right systemic arch) via a small
connecting vessel.
• However, anatomy suggests that most of its flow would be directed
towards the coeliac artery rather than the dorsal aorta.
• Secondly, left and right systemic arches communicate where they cross, via
a small foramen of Panizza in their common wall.
• The persistence of the left systemic arch and its connection from the right
ventricle to the coeliac artery and the dorsal aorta affords a pulmonary
bypass shunt

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Cardiovascular system
• Normally, blood enters the left aorta from the right aorta via the foramen
of Panizza, and the valves at the base of the left aorta remain closed to the
right ventricle because its pressure remains lower than that in the left
aorta.
• Hence, the left aorta normally carries well-oxygenated blood which reflects
its origin from the right aorta.
• However, towards the end of aerobic breath-hold dives, and probably in
anaerobic dives as well, the blood pressure rises in the right ventricle under
the influence of pulmonary circuit vasoconstriction.
• At this stage, some low oxygen blood, otherwise destined for the lungs, is
directed into the left aorta and then towards the gut; it does not mix with
any of the oxygenated blood until downstream of the dorsal confluence,
and thus preserves a well-oxygenated supply for the head and brain.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Cardiovascular system
• The shunt pathway may even allow a complete shutdown of the
pulmonary circuit, perhaps during anaerobic respiration, and the
whole body is then supported by perfusion driven by the single right
ventricle.
• Experimentally blocking both pulmonary arteries achieved this result,
with reversed flow through the foramen of Panizza, although whether
this occurs under natural circumstances is unknown.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
MAGEJA.T@VETHACKING.COM.REVISION NOTES
MAGEJA.T@VETHACKING.COM.REVISION NOTES
MAGEJA.T@VETHACKING.COM.REVISION NOTES
Cardiovascular system
• The heart
• The four-chambered heart, with a cranio-caudal orientation, is situated
between the fourth and eighth thoracic ribs.
• The apex of the heart is attached to the pericardial sac by means of a
ligament.
• A ligamentous attachment in the midline exists between the pericardial sac
and the post-pulmonary membrane.
• The post-pulmonary membrane extends to between the ninth thoracic and
first abdominal ribs.
• The dorsal part of the post-pulmonary membrane is completely
membranous, while the ventral third is muscular.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Cardiovascular system
• Left and right ventricles are separate and have a complete
interventricular septum.
• Most strikingly the left ventricle (LV) gives rise to a single aorta which
supplies the body (the right aorta (RAo), whereas the right ventricle
(RV), besides supplying the lungs via the pulmonary arteries (PAs),
also gives rise to a major vessel supplying the body, the left aorta
• The right and left aortae cross-over one another outside the
ventricles and run down the right and left sides of the body,
respectively

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Cardiovascular system
• Each has a bicuspid valve at the base the right aorta being larger than
the left
• The LAo and the RAo join twice; just outside the heart through a hole
in their joint wall (the foramen of Panizza) and by a short anastomosis
behind the heart
• The foramen of Panizza is located deep down in the valve pockets.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Cardiovascular system
• Aside from the heart and associated blood vessels, the blood system is
essentially similar to that in other reptiles.
• A renal portal system is present.
• The extensive lymphatic system is the most complex and modified among
the reptiles.
• It differs from those of other reptiles in the absence of the great sinuses
and has finer and more plexiform trunks which are generally similar to
those of mammals.
• As the flow of lymph is driven largely by hydrostatic pressure, the similarity
may reflect its association with a blood vascular system which operates at
higher pressures than those of most reptiles.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Cardiovascular system
• The spleen is pear-shaped with the broad end pointing cranially and it
is attached to the dorsal body wall between the second and third
abdominal ribs

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Cardiovascular system
• The left (LAo) and right (RAo) aortas of crocodilians communicate at
two points. The first is the foramen of Panizza (Panizza, 1833), an
aperture in the inter-aortic septum just anterior to the aortic valves.
• The second is a vessel connecting the LAo and RAo, dorsal to the
lungs, and is termed the arterial anastomosis.
• Posterior to the anastomosis, the LAo continues as the coeliac artery
to the gut, while the RAo becomes the dorsal aorta.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Nervous system and sense organs
• Before dismissing the mental capabilities of crocodilians, it is as well
to remember the complexity of their predatory and reproductive
behaviour and their homing capacities.
• Reptilian brains are about one tenth the mass of avian or mammalian
brains at comparable body size and crocodilians appear to be no
exception

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Nervous system and sense organs
• Crocodilians are well provided with sense organs, having good vision,
hearing, olfaction and senses of touch.
• The eyes are well situated for vision in air by an almost submerged
individual.
• While submerged, a translucent ‘third eyelid’, the nictitating membrane,
moves across horizontally to protect the eye.
• When underwater vision is probably restricted to sensing light and dark.
• Touch receptors and ears are probably the main operational sense organs
underwater
• The eye may be closed by depression of the upper eyelid, which is
protected by a bony scute.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Nervous system and sense organs
• Of importance in night vision is the tapetum lucidum, a layer of
retinal cells which reflects incoming light, and serves as an image
intensifying system.
• The reflective tapetum allows crocodilians to be located easily at
night, the eyes reflecting the beam of a spotlight or flashlight.
• The iris is a vertical slit by day, and opens to a wide circle at night.
• Crocodilians vocalise when in distress and during aggressive
behaviour, and are said to have excellent auditory capabilities.
• The tympanic membranes are concealed and protected by flat
rectangular flaps that may be raised and lowered by muscles

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Nervous system and sense organs
• Presumably they are closed during diving, though reception of underwater
sounds is an important aspect of social communication ref to reproduction
• Middle ear, surrounded by bone, is more complex than in other reptiles and
Olfaction originates from receptors within the nasal cavities
• The nasal cavities are the most complex among the reptiles and are essentially
similar within the Crocodylia.
• The nasopharyngeal ducts are elaborated dorsally in a series of sinuses, sacs and
blind ducts.
• Adult crocodilians lack Jacobson’s organs.
• The olfactory bulbs of the forebrain are well-developed, consistent with the
importance of olfaction.
• Taste is probably involved as well in the contact identification of food, as taste
buds occur on the tongue and posterior palate

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Urogenital system
• The kidneys are situated caudadorsally, partly within the pelvic cavity
• Mesonephric kidneys are the organs of ionic and osmotic regulation
and of nitrogen excretion, supported by the cloaca, and lingual salt
glands in the Crocodylidae but not Alligatoridae.
• All crocodilians lack a bladder.
• In fresh water, the cloacal urine is copious, clear and dilute, and
excess nitrogen is lost as ammonium ions, excreted as ammonium
bicarbonate.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Urogenital system
• The kidneys are situated caudadorsally, partly within the pelvic cavity
• The gonads lie cranio-medially to the kidneys
• Briefly, crocodilians have a complex social hierarchy which is established by
aggression and by elaborate social signalling
• Large males are dominant and territorial and are thought to fertilise most of the
females in a particular area.
• Mating occurs in the water.
• Females usually approach the male and an elaborate, sometimes prolonged
courtship ensues.
• The individuals swim together, often in circles, make body contact frequently and
rub their head over the other body (see comments on gular and paracloacal
glands).

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Urogenital system
• The female may flee a short distance, and draw the male into a chase
before circling is resumed.
• Typically females show head lifting, submissive postures.
• Copulation occurs when the male curls his tail under the female, lying to
the side. In shallow water, both individuals may be seen lying on their
sides.
• All Alligatoridae, half of the Crocodylidae and Tomistoma nest in mounds.
• The remaining species use holes.
• Crocodylus acutus nests sometimes in a hole and sometimes in a mound.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Urogenital system
• Mound nesters lay their eggs in a nest constructed from grass or other
vegetation, litter, and sand or soil in various proportions, depending upon
what is available at the site
• The mound is constructed using material dug up with the hind legs, or from
vegetation torn off with the teeth.
• Eggs are laid about six weeks after mating into a hole which is dug with the
hind feet into the sandy substrates of a river bank.
• Though incubation time is temperature dependent, under average field
conditions C. johnstoni hatch after about eleven weeks.
• Crocodylus porosus is a mound nester and, unlike C. johnstoni, breeds in
the wet season.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Urogenital system
• After courtship at the end of the dry season, nests are built at the
onset of ‘the wet’.
• If the wet season begins early, the nesting season may be quite
prolonged and tapers off towards March and April.
• Crocodylus porosus lays 50 to 60 eggs, which are heavier than those
of C. johnstoni, weighing about 100 g (range 70 to 140).
• The number and size of the eggs reflects the age and size of the
mother.
• At normal field temperatures, incubation takes about 80 to 90 days.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Urogenital system
• The single, rigid penis is pulled out and forward by muscles.
• A middorsal, open groove receives sperm through juxtaposition with
the vasa deferentia, which open dorso-laterally through the cloacal
wall.
• The testes are paired and adjacent to the kidneys.
• They undergo a conspicuous annual cycle in size and activity .
• The clitoris of females is much smaller than the penis, but lies in the
same position.
• The oviducts open anteriorly to receive ova from the paired ovaries,
adjacent to the kidneys.

MAGEJA.T@VETHACKING.COM.REVISION NOTES
Urogenital system
• Each of the two oviducts opens into the cloaca via a vagina with a
narrow lumen which spirals through the muscular cloacal walls
• How these walls relate functionally to the role of a vagina as a
receptacle for a penis, is unclear and the appropriateness of the term
is uncertain.

MAGEJA.T@VETHACKING.COM.REVISION NOTES