8. The Posterior palatine vacuities. Each is bounded by the maxillae in front, the maxillae and transpalatine externally, the transpalatine and pterygoid behind, and the palatine on the inner side (fig. 43, A, 7).
9. The Anterior palatine vacuity. This is unpaired and is bounded by the premaxillae (fig. 43, A, 8).
(b) The Lower Jaw or Mandible.
The mandible is a strong compact bony structure formed of two halves or rami, which are suturally united at the symphysis in the middle line in front. Each ramus is formed of six separate bones.
The most anterior and largest of these is the dentary (figs. 44, 20, and 45, 18), which forms the symphysis, and greater part of the anterior half of the jaw, and bears along the outer part of its dorsal border a number of sockets or alveoli in which the teeth are placed. Lying along the inner side of the dentary is a large splint-like bone, the splenial (fig. 45, 19), which does not extend so far forwards as the symphysis, and is separated from the dentary posteriorly by a large cavity. Forming the lower part of all the posterior half of the jaw is the large angular (figs. 44, 22, and 45, 20), which underlies the posterior part of the dentary in front and sends a long process below that bone to the splenial. On the inner side of the jaw there is an oval vacuity, the internal mandibular foramen (fig. 45, 28), between the angular and the splenial; through this pass blood-vessels and branches of the inferior dental nerve. Lying dorsal to the angular is another large bone, the supra-angular (figs. 44, 18, and 45, 21). It extends back as far as the posterior end of the jaw and forwards for some distance dorsal to the dentary and splenial. It forms part of the posterior margin of a large vacuity, the external mandibular foramen, which is bordered above and in front by the dentary and below by the angular; it gives passage to the cutaneous branch of the inferior dental nerve. The concave surface for articulation with the mandible and much of the posterior end of the jaw is formed by a short but solid bone, the articular (fig. 45, 22), which in young skulls rather readily becomes detached. The remaining mandibular bone is the coronoid (fig. 45, 23), a very small bone of irregular shape attached to the angular below, and to the supra-angular and splenial above.
(c) The Hyoid.
The hyoid of the Crocodile consists of a wide flattened plate of cartilage, the basilingual plate or body of the hyoid, and a pair of cornua.
The basilingual plate (fig. 53, 1) is rounded anteriorly and marked by a deep notch posteriorly. The cornua (fig. 53, 3), which are attached at a pair of notches near the middle of the outer border of the basilingual plate, are partly ossified, but their expanded ends are formed of cartilage. They pass at first backwards and then upwards and inwards. They are homologous with part of the first branchial arches of Selachians.
The columella and extra-columella have been already described (p. 251).
C. The Ribs and Sternum.