Page:The Osteology of the Reptiles.pdf/33

Rh or fused with the premaxillae in the Mosasauria (Fig. 54 ); separated by the premaxillae in the plesiosaurs, pterosaurs (Fig. 72), and some lizards (Fig. 56), and probably absent in some of the former (Fig. 46). They do not enter into the formation of the nares in the Rhiptoglossa (Fig. 55 ), but surround them in the Phytosauria (Figs. 66, 67). Very large in the Ichthyosauria (Fig. 50), they also articulate with the large postfrontals. They are often fused in the midline.

Frontals (fr). Primitively (Figs. 2, 4, 22, 23, etc.) articulating with nasals, prefrontals, postfrontals, parietals, and ethmoids, often forming the middle of the upper margin of the orbits.

Always present and not varying much in their relations. In the plesiosaurs (Fig. 46), pterodactyls (Fig. 72), and some lizards, they articulate directly with the premaxillae (Fig. 56), and in some of the former are separated externally in the middle. Often fused in midline (Figs. 68, 69).

Parietals (pa). Primitively (Figs. 2, 4) articulating with frontals, postfrontals, intertemporal, supratemporals, tabulars, and interparietals; below with the supraoccipital, epipterygoids, postoptics, and proötics.

In the absence (e.g., Figs. 31, 33, 44, 45, etc.) of the intertemporal and supratemporals, the parietals articulate directly with the squamosals and postorbitals; in the Chelonia (Fig. 30) and Crocodilia, also directly with the pterygoids. Fused in most late reptiles (e.g., Figs. 69, 72).

Interparietals (ip). Primitively (Figs. 2, 4, 22) back of the parietals on the superior surface of the skull, articulating with parietals, tabulars, and supraoccipital.

In the later Cotylosauria (Fig. 9), most if not all Theromorpha (Figs. 33, 42 ), some Therapsida (Figs. 44 ), they are situated on the occipital surface and are usually unpaired. A vestige, supposed to be these bones, occurs in some Crocodilia, originally named dermosupraoccipitals. They do not help form any part of the cerebral wall. Unknown or doubtful in other reptiles.

Lacrimals (la). Primitively (Figs. 2, 3, 22, 23, etc.) large, extending from orbit to nares, articulating with prefrontals, nasals, septomaxillae, maxillae, and jugals.

In the latest Cotylosauria (Procolophon), most Theromorpha