Page:The Osteology of the Reptiles.pdf/35

Rh Ichthyosauria (Fig. 50). Thought by some to be the homologues of the mammahan lacrimals, and so called.

Postfrontals (pf). Primitively (Figs. 2, 4, 22) at the upper posterior border of the orbits, articulating with prefrontals, frontals, parietals, the intertemporal or supratemporals when present, and with the postorbitals.

In the Chelonia (Figs. 30, 31 , 32 ), Crocodilia (Figs. 68, 69), many mosasaurs (Fig. 54), lizards (Fig. 56) and the snakes (Fig. 59), the Pterosauria (Figs. 71, 72), Dinosauria (Fig. 70), and many Therapsida (Figs. 44 , 45), they are absent or fused with the postorbitals which take their place. Sometimes they (Fig. 46, 49 ) help form the anterior boundary of the upper temporal opening. They extend forward to the nasals in the Ichthyosauria (Fig. 50).

Postorbitals (po). Primitively (Figs. 2, 3, 4, 5, 22) at the upper back part of the orbits, articulating with postfrontals, jugals, and squamosals. A descending process also articulates with the maxillae or ectopterygoids.

In the absence of the intertemporal and supratemporal, the postorbitalalso articulates with the parietal (Figs.28, 30, 33, 43). In the absence of the postfrontal it takes its place, often extending forward to meet the prefrontal (Figs. 30, 45 ), or even the lacrimal (Fig. 70 ) in the Theropoda. It still retains its connection with the maxillae [sic] in certain Chelonia (Fig. 31 ) and most snakes (Fig. 59), but not in most other reptiles. Rarely in the lizards (Fig. 56) it does not meet the squamosal. In the Crocodilia (Fig. 69) it is large, and may articulate with frontal, parietal, jugal, quadratojugal, and squamosal. It extends far back in the Chelonia (Figs. 30, 31 ), forming a large part of the temporal roof, articulating with the quadratojugal, the latter also in the Ichthyosauria (Fig. 50). It is extensive also in some of the Dinosauria (Fig. 70), supporting the paired horns of the Ceratopsia (Fig. 70 ).

Jugals (ju). Primitively (Figs. 2, 3, 5, 22, 33) large, forming the under boundary of the orbits, articulating in front with lacrimals