SKULL — BIRDS 



169 



suture to squamosal, quadratojugal and pterygoid, but may have had slight 

 motion in some species. It extends downwards and forwards so that in some the 

 hinge of the lower jaw is beneath the orbit. All, except the Ceratopsia, lack a 

 coronoid process. The tip of the lower jaw of Ornithischians (fig. 182, B) 

 is formed by a predentary bone, peculiar to this group. 



Fig. 182. — Skulls of Dinosaurs. .4, Ornilholesies hermanni (Osborn, "16); B, 

 Camplosaurus (Gilmore, '09). an, angulare; av, antorbital vacuity; d, dentale; e, 

 exoccipital;/, frontal; /, lacrimal; mx, maxilla; n, nasal; wo, naris; o, opisthotic; or, orbit; 

 p, parietal; pd, predentary; pf, prefrontal; pm, premaxilla; po, postfrontal; g, quadrate; 

 sq, squamosal; st, supratemporal fossa; s, zygomatic. 



AVES. — The bird's skull is most closely related to that of reptiles, 

 the resemblance being most marked in the single occipital con- 

 dyle, largely or wholly on the basioccipital; the suspensorial quadrate, 

 the usual antorbital vacuity; and the tropibasic chondrocranium. 

 But there are marked differences, the most noteworthy being corre- 

 lated with the greater development of cerebrum and cerebellum which 

 has caused a great vaulting of the cranial roof and a widening of its 

 sides, resulting in the entrance of the squamosal into the wall of the 

 cranial cavity, between parietal, exoccipital and prootic. The back- 

 ward extension of the brain and the non-horizontal neck have 



