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).
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.
The ribs are short imperfectly ossified structures, bifid at their proximal end where they articulate with the transverse processes, and tipped both proximally and distally with cartilage. The dorsal portion of the proximal end corresponds to the =tuberculum= of the ribs of higher animals, and the ventral portion to the =capitulum=. Some of the anterior ribs have a step-like notch on their dorsal surfaces.