XI 



SKELETON 



485 



and extend forwards as slender bones to the vomer, separating 

 the palatines. The choanae are enclosed by the vomer, palatines, 

 and maxillaries, and they lie in dorsal recesses above the level 

 of the roof of the mouth. The teeth are alveolar, pointed, of 

 variable size, and restricted to the jaws ; in the Pteranodonts 

 they are absent. 



The brain is known from the natural cast of Scaphognathus, 

 and shows some remarkably bird-like features, especially the 

 width of the hemispheres, which touch the well- developed cere- 

 bellum, while the optic lobes lie on the sides of the cerebellum, 

 with a pair of appendices, the so-called flocculi, elsewhere known 

 in birds only. 



The caudal vertebrae are still amphicoelous, while the pre- 

 sacral vertebrae are procoelous. 

 Abdominal ribs are few in number 

 and are very thin. The true ribs 

 possess capitula and tubercula ; 

 those of the neck are very short 

 and directed backwards ; in the 

 thoracic region they are long, and 

 some are attached to a broad 

 sternum with a keel and a median 

 anterior process, on the sides of 

 which latter articulate the cora- 

 coids, Precoracoids and clavicles 

 are absent. The scapulae are long, 

 sabre-shaped, and turned back as 

 in birds ; in Pteranodon they show the unique modification of 

 articulating with special processes of the neural arches of several 

 ankylosed thoracic vertebrae. 



The hand possesses only four fingers ; the four phalanges of 

 the ulnar finger are very much elongated for the support of the 

 patagium ; the other fingers remain short and are provided with 

 little claws. The ilia are expanded horizontally, and are firmly 

 attached to from three to six vertebrae, which mostly fuse together 

 into a sacrum. The ventral half of the pelvis consists of a pair 

 of broad bones, which contain a small obturator-foramen ; they 

 form a ventral symphysis, and are usually fused with the ilium. 

 These bones represent the conjoint ischia and pubes, while the 

 so-called pubes, a pair of flat and club-shaped bones, are excluded 



FIG. 116. Pterodactylus crassirostris. 

 x |. (From Geikie.) 



