The =articular= (fig. 38, 11) is expanded, and with the _supra-angular_ forms the concave articulating surface for the quadrate.
The _splenial_ (fig. 38, 10) is a thin plate applied to the inner surface of the posterior part of the mandible.
The _angular_ (fig. 38, 13) is a slender plate of bone lying below the supra-angular and splenial.
The hyoid apparatus is well developed, parts of the first two branchial arches being found, as well as of the hyoid proper. It consists of a more or less oblong flattened =basilingual plate= or =body of the hyoid= which represents the fused ventral ends of the hyoid and branchial arches of the embryo, and is drawn out into a point anteriorly. The greater part is formed of unossified cartilage, but at the posterior end it is bilobed, and a pair of ossified tracts occur. To its sides are attached three pairs of structures, which are portions of the hyoid and first and second branchial arches respectively.
The free part of the =hyoid= consists of a small piece of cartilage attached to the anterior part of the basilingual plate at its widest portion (fig. 53, 2).
The =anterior cornu= or free part of the =first branchial arch= is much the largest of the three structures. Its proximal portion adjoining the basilingual plate is cartilaginous, as is its distal end; the main part is however ossified.
The =posterior cornu= or free part of the =second branchial arch= (fig. 53, 4) consists of a short flattened cartilaginous bar arising from the bilobed posterior end of the basilingual plate.
The hyoid apparatus has no skeletal connection with the rest of the skull.
This includes the skeleton of the two pairs of limbs and their girdles.
The pectoral girdle has an anomalous position, being situated internal or ventral to the ribs. It consists of three bones, a dorsal bone, the =scapula=, an anterior ventral bone, the =precoracoid=, and a posterior ventral bone, the =coracoid=.
The =scapula= is a small somewhat rod-shaped bone forming about two-thirds of the glenoid cavity. At its proximal end it is closely united with the precoracoid, the two bones ossifying continuously. It tapers away distally, and is directed dorsalwards towards the carapace.
The =precoracoid= forms an angle of about 130° with the scapula, with which it is completely fused at its proximal end. Its distal end is somewhat expanded and flattened, and is terminated by a fibrocartilaginous =epiprecoracoid= which meets its fellow. It takes no part in the formation of the glenoid cavity.