EXPERIMENT 1: STUDY OF OSTEOLOGY OF

FROG

MATERIAL REQUIRED:
1. Laboratory manual of the laboratory course BZYCL-134,
2. Complete articulated skeleton of frog,
3. Dorsal and ventral parts of the skull of frog,
4. Disarticulated vertebral of the vertebral column of frog,
5. Disarticulated bones of appendicular skeleton of frog,
6. Pen, pencil, sharpener, eraser and measuring scale,
7. Hand lens,
8. Notebook.

The skeleton of frog shows that it is a tetrapod and that it can be divided into
two parts the:
(1) Axial skeleton which comprises of: i) bones of the head (skull); and
ii) bones of the trunk, which include the vertebral column, and thorax;
and
(2) Appendicular skeleton which comprises: i) the bones of the paired
limbs, namely the forelimbs and the hind limbs; and ii) the pectoral
(shoulder) and pelvic girdles.

Skull and Jaw Bones of Frog

The skull and jaws of frogs serve to protect the brain and the special sense
Organs

1. Skull is formed mostly of bony tissues but tadpole skull is cartilaginous.

2. Skull consists of cranium, sense capsules, jaws and hyoid apparatus.
3. The frog skull includes three regions i.e. cranium (brain box), sense
capsules and jaws.
4. The skull is divided into auditory, olfactory and occipital regions.
5. The ethmoidal region is absent.
6. In frog the skull is triangular in shape, broad and dorsoventrally flattened.
7. The front part of the cranium which houses the eyes, nose and the brain
is much better developed whereas the back portion is much reduced.
8. The neurocranium or simply called cranium or brain box which encloses
the brain is much smaller than the mammals due to the smaller size of
brain.
9. The dorsal part of the cranium is formed by the frontoparietal bone. The
ventral part of the cranium is formed by the parasphenoid bone while the
lateral sides are formed by paired sphenethmoid bones.
10. Floor of cranium is formed by paraphenoid bones and the roof by
frontopareital bones.
11. Posterior most part of the cranium is the occipital segment, and is mainly
made up of a pair of occipital condyles called exoccipitals on the lateral
side which enclose posteriorly an opening called foramen magnum.
The frog skull is thus, dicondylic skull due to the presence of paired
occipital condyles.
12. The interorbital septum is absent in the skull so the cranium extends
beyond the eye orbits.
13. The paired eye orbits are dorsally placed and they are not fused with the
skull.
14. A pair of olfactory capsules is present. The olfactory capsules are
separated, from each other by the mesethmoid both. Each capsule is
formed by a large triangular nasal bone on the dorsal side and smaller
triradiate vomer bones on the ventral side. The vomers possess
vomerine teeth.
15. Paired auditory capsules are present, each enclosing an internal ear.
The anterior wall and partly the roof and floor of each auditory capsule
is formed by the irregular cartilage pro-otic bone and squamosal.
16. Branchial arches are absent in the skull.
Exercise 1 Study of Osteology of Frog: Disarticulated Skeleton
11
17. The upper and lower jaws are present which support the borders of the
mouth.
18. The upper jaw is formed by union of two similar halves. Each half is
formed by the pre-maxilla, maxilla and quadratojugal bones. The
inner set of the jaw has palatine, pterygoid and squamosal bones.
19. The maxilla bones of the upper jaw is provided along its whole length
with numerous sharp, pointed and backwardly directed conical teeth
(homodont dentition).
20. The lower jaw or mandible consists of two halves which are united
anteriorly by mento-meckelian cartilage. Each half of the lower jaw
consists of a core of Meckel's cartilage surrounded by three bones i.e.
Mentomeckelian, angulosplenial and dentary.
21. The lower jaw on mandible is devoid of teeth.
22. Jaw suspensorium is autostylic, in which the lower jaw is attached to
skull through a rod like cartilaginous quadrate bone
VERTEBRAE OF FROG
It consists of only nine vertebrae, the last one followed by a slender bony rod, the urostyle. The
first vertebra that articulates at its proximal end with skull is termed as the Atlas vertebra. The
2nd to 7th vertebrae have similar structure and hence are called as typical vertebrae.

ATLAS VERTEBRA
1. The atlas vertebra is the first vertebra of the vertebral column.
2. The transverse processes and prezygapophyses are absent.
3. Anteriorly the centrum has a pair of large concave facets in order to
articulate proximally with the occiptal condyles of the skull.
4. Postzygapophyses are present on the posterior margins of the neural
arch.

TYPICAL VERTEBRA
(Second to Seventh)
1. The structure of 2nd to the 7th vertebrae of frogs is similar or typical
2. Each typical vertebrae has a ring-like form with a large passage called
the neural canal through which the spinal cord passes.
3. In all typical vertebrae, the centrum is procoelus (pro: front, coelous:
cavity) and so its anterior side is concave and the posterior face is
convex (to fit into the concavity of the centrum of the next vertebra).
4. Neural arch is present and bears a small and blunt middorsal neural
spine which is directed obliquely backwards.
5. At the base of neural spine on either side the neural arch bears
anteriorly, the upwardly and inwardly directed articular surfaces called
prezygapophyses.
6. The postzygapophyses are present at the posterior margins of the
neural arch and are directed downwards and upwards (to fit into the
prezygapophyses present on the next vertebra).
7. Prominent, tapering processes directed sidewards arise from the neural
arches and are called the transverse processes.
8. Now look at the second and fourth vertebra in particular. The second
vertebra (Fig 1.6 a) is like the other typical vertebrae except that its
neural spine is short and conical and its transverse processes are broad
and flat.
9. The fourth vertebra (Fig 1.6 b) is also like all the other typical vertebrae
except that the transverse processes are broader.

Eighth Vertebra
i) The eighth vertebra closely resembles a typical vertebra but its centrum
is amphicoelus or biconcave
(ii) Its anterior concavity receives the posterior convexity of the 7th vertebra
while its posterior concavity receives the anterior convexity of the 9th
vertebra.

Ninth Vertebra
1. The ninth vertebra is also called the sacral vertebra and
is different in many respect from the other vertebrae present in the
vertebral column of frog.
2. Its centrum is biconvex and bears one anterior and two posterior
convexities.
3. The two posterior convexities fit into the corresponding two anterior
concavities of the urostyle distally.
4. Large cylindrical and stout transverse processes which are directed
backwards are present on the sacral vertebra.
5. The distal ends of these transverse process support the iliac bones of
the pelvic girdle.

Urostyle
1. The urostyle (Gr. Oura,Tail + Stylos, Pillar) is the posterior,
unsegmented part of the vertebral column representing the fusion of the
caudal vertebrates. It is half of the total length of vertebral column of
frog.
2. The urostyle is somewhat triangular in outline, with a pointed apex
directed backwards.
3. Its centrum is rod-like with a broad anterior face bearing two concavities
for articulating proximally with the distal end of the ninth vertebra.
4. The dorsal surface of the urostyle is raised up in the form of a vertical
ridge which gradually tapers posteriorly.
5. The anterior side of the ridge of the urostyle contains a short narrow
neural canal which encloses the terminal part of spinal cord.

STERNUM AND RIBS

1. The sternum lies in the midventral line and is connected intimately with the two halves of the
pectoral girdle.
2.The sternum provides ventral protection for the heart and lungs and
includes four parts: (a) episternum, (b) omosternum, (c) mesosternum
and (d) xiphisternum.

The episternum is a flat circular and cartilaginous disclike bone, and is

anterior most in position.
The ornosternum is a bony rod that connects the episternum with the
clavicles.
The mesosternum is a cartilaginous rod that projects behind the epicoracoid.
The xiphisternum is thc terminal, broad, cartilaginous plate.
Pectoral Girdle
1. The pectoral girdle protects the inner softer parts of the chest
region as there are no ribs. The pectoral girdle also provides support and
attachment to the forelimb bones and muscles.
2. The pectoral girdle is formed of both bones and cartilages.
3. The two similar halves of pectoral girdle are united midventrally with the
sternum but are separated dorsally.
4. Each half is made up of four bones: (a) supra-scapula, (b) scapula, (c)
coracoid and (d) clavicle bones.
5. Supra-scapula is a broad, flat, almost rectangular bone in which the
calcified cartilage is absent from its upper margin.
6. The scapula is a stout, flat bone which is broader towards tail end and is
constricted in the middle.
7. Posteriorly, the scapula forms the upper half of glenoid cavity. The head
of the humerous of the forelimb articulates with glenoid cavity of the
pectoral girdle.
8. The clavicles and coracoids of both sides unite with each other
midventrally and with sternum through a cartilaginous strip called
epicoracoid.
9. The clavicle is a slender rod-like bone separated from the coracoid by a
wide gap called coracoid foramen.
10. A narrow strip of cartilage called the precoracoid, lies attached to each
clavicle posteriorly.
11. The coracoid is a dumb-bell shaped bone with its inner end broader than
the outer end.
12. The outer end of the coracoid forms the lower half of the glenoid cavity
which receives the head of humerus bone of the forelimb.
Pelvic Girdle
1. The frog pelvic girdle is a 'V' shaped structure present in the
posterior region of the body and is composed of two similar halves. The
pelvic girdle provides support to the pelvic region and the hind limbs.
2. Each half of the pelvic girdle is called as os-innominatum and is
composed of three bones: (a) ilium, (b) ischium and (c) pubis:
3. The long ilium meets with the transverse processes of the ninth vertebra.
4. The two ilia meet posteriorly at an iliac symphysis. The two ilia bear a
prominent, dorsal vertical ridge called the iliac crest.
5. The pubis is much reduced. It is a triangular piece of calcified cartilage
which forms the central disc of pelvic girdle and a small part of the
acetabulum cavity in which the head of femur of the hind limb is lodged.
Both the pubic bones are completely fused together.
6. The two ischia are larger and slightly central oval bones. Both the ischia
fuse in the middle and form one third of the disc and acetabulum.
7. The disc of the pelvic girdle is thus formed by the union of three bones :
ileum, ischium and pubis and contain a cup-shaped cavity called the
acetabulum.

LIMBS OF FROG (Forelimbs)

The humerus, radio-ulna and hand bones constitute the bones of the forelimb

HUMERUS BONE

1. It is a short cylindrical bone of the upper arm.

2. The shaft of the humerus is slightly curved
3. At the proximal end the round head of the humerus bone is
present which fits into the glenoid cavity of the pectoral girdle.
4. The head of the humerus is covered by calcified cartilage. A
deltoid ridge for the attachment of muscles is present below the
head of the humerus bone.
5. The distal end of the humerus has a well developed prominent
trochlea or capitulum and a condylar ridge for articulation with
radio-ulna.
RADIO-ULNA BONE

1. The radio-ulna bone forms the lower arm of the forelimb. It is a

compound bone formed by the fusion of two bones namely, radius
and ulna.
2. A concavity is present at the proximal end of the radio-ulna bone to
receive the rounded trochlea of the humerus.
3. The proximal portion of ulna has a projection called the olecranon
process which forms the elbow joint.
4. Distally the division of the radio-ulna into radius and ulna bones is
well marked due to the presence of a groove.
5. Each of these bones of the lower arm terminate distally into a facet
to articulate with the carpal bones of the hand.

THE HAND OF THE FORELIMB

1. The wrist bones called the carpals are 6 in number and are arranged into
two rows
2. The proximal row of carpals has three carpal bones : radiale,
intermedium and ulnare which articulate at the proximal end with the
distal end of the radio-ulna bone
3. The distal row of carpals is formed of three other bones called
trapezium, trapezoid and capitohematum which articulate distally with
the metacarpal bones.
4. Five, slender, rod-like bones the metacarpals form and support the hand
of frog and articulate proximally with the distal end of the second row of
carpal bone. The first metacarpal bone is rudimentary.
5. There are only four digits in the hand of the frog as the pollex or thumb is
absent
6. All the four digits are internally supported by short rod-like bones called
phalanges.
7. Two phalanges are present in each of the first and second digits and
three phalanges are present in each of third and fourth digit.
LIMBS OF FROG (Hindlimbs)
Femur, tibio-fibula, astragalus-calcaneum and foot bones constitute the hind
limb of the frog

FEMUR BONE

1. Femur or the thigh bone is the first bone of the hindlimb.

2. It has a slightly curved shaft and has expanded ends that are
covered by calcified cartilage.
3. The proximal end of the femur has a rounded head which
articulates with acetabular cavity of pelvic girdle.
4. The distal end of the femur articulates with the proximal end of the
tibio-fibula which is the shank bone and forms the lower part of the
hind limb.

TIBIO-FIBULA

1. This is a large compound bone of the shank, and is the longest

bone in the frog skeleton.
2. Its shaft is slightly curved while the two ends are expanded and
are covered by cartilage.
3. As indicated by the median longitudinal groove, this bone is made
up of two bones i.e. inner tibia and outer fibula.
4. The proximal end of tibia contains a tibial crest.
5. The tibio- fibula bone articulates proximally with femur and distally
with astragalus calcaneum.

ASTRAGALUS-CALCANEUM

(i) Astragalus and calcaneum together constitute a compound tarsal

bone.
(ii) The astragalus-calcaneum tarsal bones are greatly elongated and
represent two rows of tarsals that are fused together at proximal
and distal ends but have a wide gap at the middle.
(iii) The outer thicker and straight bone is called calcaneum while the
inner, thinner and slightly curved bone is the astragalus (or tibiale).
(iv) Both ends of the astragalus-calcaneum tarsal bone are covered by
epiphysis or calcified cartilage.
(v) The distal row of tarsals bears two very small tarsal bones.

BONES OF FOOT

(i) The foot of frog is supported by five long slender metatarsals.

(ii) These metatarsals have 5 true digits (toes) and in addition a very
small pre-axial sixth toe, which is present on the inner side of the
1st toe or hallux.
(iii) This supplementary small pre-axial sixth toe is called calcar or
prehallux or false toe. It is made of 2-3 small bones and does not
project from the foot.
(iv) The true toes have 2, 2, 3, 4 and 3 phalanges respectively.