The alligator and its allies

by A. M. Reese

The supra-angular ([Figs. 23] and [24], 21, [Fig. 21], 18) is an elongated bone that forms the dorsal border of the external mandibular foramen; it also forms the lateral edge of the articular surface for the quadrate. It articulates anteriorly with the splenial, the dentary, and the coronoid; and posteriorly with the angular and articular.

The articular ([Figs. 23] and [24], 22, [Fig. 21], 19), which is scarcely visible in a lateral view, forms most of the surface for articulation with the quadrate, and sends back the large process so characteristic of the crocodilian skull. On the dorsal side of this process is a concavity that looks like another articular surface. Laterally the articular articulates with the supra-angular; ventrally and posteriorly with the angular.

The angular ([Fig. 23], 20, [Fig. 21], 22) forms the ventro-posterior border of the jaw and of the external mandibular foramen. Its narrow, posterior end forms a part of the prominent process mentioned in connection with the articular. Between it and the posterior edge of the splenial is the internal mandibular foramen, which is much smaller than the external ([Fig. 23], 28). Anteriorly the angular articulates with the dentary, coronoid, and splenial; dorsally with the supra-angular and the articular.

The Hyoid

([Fig. 25]). The hyoid being mainly of cartilage is usually not seen in prepared skeletons. It is thus described by Reynolds:

“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. 25], 1) is rounded anteriorly and marked by a deep notch posteriorly. The cornua ([Fig. 25], 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.”

Fig. 25. Hyoids of an Alligator (Caiman latirostris) (TO THE LEFT) and of a Green Turtle (Chelone midas) (TO THE RIGHT). ×⁵⁄₈. (Brit. Mus.) (After Reynolds.)

The cartilaginous portions are dotted.