The teeth are exoskeletal structures, partly of dermal, partly of epidermal origin. They lie along the margins of the jaws and are confined to the premaxillae, maxillae and dentaries. They are simple conical structures, without roots; each is in the adult placed in a separate socket, and is replaced by another which as it grows comes to occupy the pulp cavity of its predecessor. In the young animal the teeth are not placed in separate sockets but in a continuous groove. This feature is met with also in the Ichthyosauria. The groove gradually becomes converted into a series of sockets by the ingrowth of transverse bars of bone. The anterior teeth are sharply pointed and slightly recurved, the posterior ones are more blunt.
The upper jaw bears about nineteen pairs of teeth, the lower jaw about fifteen pairs. The largest tooth in the upper jaw is the tenth, and in the lower jaw the fourth.
The three living families of Crocodilia, the Crocodiles, Alligators and Garials, can be readily distinguished by the characters of the first and fourth lower teeth. In Alligators both first and fourth lower teeth bite into pits in the upper jaw; in Garials they both bite into notches or grooves in the upper jaw. In Crocodiles the first tooth bites into a pit, the fourth into a notch in the upper jaw.
II. ENDOSKELETON.
1. The Axial Skeleton.
This includes the vertebral column, the skull, and the ribs and sternum.
A. The Vertebral column.
The vertebral column is very long, consisting of some sixty vertebrae. It can be divided into the usual five regions, the cervical, thoracic, lumbar, sacral, and caudal regions.
Fig. 41. First four cervical vertebrae of a Crocodile (C. vulgaris). (Partly after von Zittel.)