Osteology (frog, rabbit, fawl, varanus), Study notes of Zoology

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The living Amphibia do not possess an exoskeleton. The endoskeleton of frog is made partly of cartilage and partly of bone. In the early stages of development (tadpole), the skeleton is solely cartilaginous but, in the adult frog, it is greatly replaced by bones called the cartilage or replacing bones. Bones become also developed in other parts of skin or dermis of certains regions where there was no pre- existing cartilage. Such bones are termed membrane bones, A part of primary cartilaginous skeleton is impregnated by calcium salts and becomes hard. This is known as the calcified cartilage, As usual, the skeleton is conveniently divided into axial and appendicular skeleton, Axial skeleton includes skull, vertebral column and sternum which lie along the median longitudinal axis of body. Appendicular skeleton comprises the skeleton of the limbs and the girdles supporting them (Fig. 1). CHARA STIC FEATURES SKULL ee Skull of frog is characterized by the following important characters : (1) It is triangular in shape, broad and dorso-ventrally flattened. (2) A considerable part of chondrocranium of tadpole persists in the adult. A large part of cranium and sense capsules consists of cartilage. . (3) Cranium is comparatively small and narrow due to small size of brain which it encloses.