Question

The interclavicle in reptile is
A. H-shaped
B. W-shaped
C. T-shaped
D. A-shaped

Answer 1

Hint: The bone between the clavicles (collar bones) and above the sternum, present in all four-limbed animals (tetrapods) is called an interclavicle (also known as entoplastron). The interclavicle is developed by the intramembranous ossification of the skin. It is a membranous bone present in the mid-ventral region. It is present in all reptiles except snakes and monotremes.

Complete answer:
The interclavicle bone is generally ‘T’ shaped in most of the tetrapods which prolongs the sternum anteriorly. It varies from within various organisms. A true T-shaped interclavicle occurs in mammals.
Some of the variations in the interclavicle of reptiles are as follows:
-The interclavicle in the ancestral reptiles was elongated bone with dilation but did not consist of a T-shaped anterior extremity.
-The stem is underlined by the mesial borders of the coracoids.
-Pantlus (primitive reptile) comprised a forked interclavicle in front with fan-shaped behind, resembling that of monotremes.
-The modern reptiles comprise extended dilation in the front end.
-In therapsida the shape of the interclavicle resembles Theromorpha and Cotylosauria.
-Lystrosaurus comprises short and fan-shaped interclavicles.
-In crocodile its slender and free at the anterior end-‘A’ shaped
-Ichthyosauria comprises short stems.
-Nothosauria comprises vestigial interclavicle
-Pterosauria, Dinosauria, chameleon lizards and some of the plesiosaurs do not possess interclavicle
Thus the interclavicle in reptiles is ‘A’ shaped. Hence, the correct answer is option (A).

Note: In birds the interclavicle is incorporated within the clavicles of the body, and is called the hypoclidium (furcula). In reptiles the interclavicle is distinct from the clavicles of the body and in frogs it is represented by the omosternum. In fishes the interclavicle is an intermediate element of the scapular arch.