The premaxillae are united, forming a single bone, which in a ventral view is seen to meet the maxillae and vomero-palatines, and in a dorsal view to send back a nasal process (fig. 21, A, 1) between the nasals.
The maxillae are large bones, each terminating in a point posteriorly. A single row of teeth similar to those on the vomero-palatines runs along the outer margin of the maxillae and premaxillae.
The posterior part of the upper jaw forms a mass of cartilage which extends forwards towards the maxillae as a long pointed process whose ventral surface and sides are overlapped by a membrane bone, the pterygoid (fig. 21, 12).
The suspensorial bones include the quadrate and squamosal. The quadrate (fig. 21, 15) which forms the true suspensorium is directed forwards and outwards, and is terminated by a patch of cartilage with which the mandible articulates.
The lower jaw or mandible remains partly cartilaginous, while its ossifications include two membrane bones and one cartilage bone. The cartilage bone is the articular (fig. 21, C, 18), it forms the posterior part of the ramus, extends forwards for some distance along its inner side, and is terminated posteriorly by a patch of cartilage which articulates with the quadrate. The dentary (fig. 21, C, 20) is a large bone which forms the anterior part and nearly all the outer half of each ramus, and bears teeth similar to those of the upper jaw. Attached to its inner face is a long slender splenial (fig. 21, C, 21).
The Hyoid apparatus.
This consists of the hyoid arch and part of the first two branchial arches.
The hyoid arch (fig. 29, A, 2) consists of a pair of cornua, each of which is divided into two halves. The dorsal half forming the cerato-hyal is mainly ossified though tipped with cartilage, and is connected by ligament with the suspensorium. The ventral half (hypo-hyal) is cartilaginous, and is connected with the basibranchial.
The branchial arches consist of a median piece, the basibranchial, which is ossified in the centre and cartilaginous at either end, and of two pairs of cerato-branchials which are attached to the cartilaginous part (fig. 29, A, 8) of the basibranchial. The first cerato-branchial is chiefly ossified, the second (fig. 29, A, 4) is a good deal smaller and is cartilaginous. Both are united dorsally to a single epi-branchial, which is terminated by a small cartilaginous area at the free end but is elsewhere well ossified.
C. The Ribs.