ORDER VIII DINOSAURIA 225 



the brain cavity is exceedingly diminutive. The latter, in proportion to the 

 size of the head, is smaller in Triceratops than in any known land vertebrate. 

 Among the Theropoda and Predentata the long axis of the skull is approxi- 

 mately at right angles to the neck, but in the quadrupedal Saiiropoda it 

 continues the line of the vertebral column. The large orbits are laterally 

 directed, and between them and the paired narial openings is frequently an 

 antorbital vacuity, as in crocodiles, pterosaurs, and birds. The temporal 

 vacuities are completely enclosed, and vary considerably in form and size. 

 The large quadrate is prominently exposed, and suturally united with the 

 squamosal and quadrato-jugal. The paired premaxillae are rather extensively 

 developed, and either provided with teeth, or edentulous and beak-like. 



The inferior aspect of the skull is similar in a general way to that of 

 Rhynchocephalians, except that there are no teeth on the palate. The 

 mandibular rami are united in a cartilaginous Symphysis, and in the Pre- 

 dentata a crescentic, edentulous, predentary bone is developed in front of the 

 mandible, the sharp margin of which appears to have been sheathed in a 

 horny beak. Teeth are confined to the margin of the jaws, and are either 

 deeply socketed or implanted in an alveolar groove open on the inner side of 

 the jaws. 



In the pedoral arch clavicles appear to be wanting, and the sternum is 

 imperfectly ossified. The scapula is very strongly developed, and usually 

 much elongäted. The coracoid is flattened, with more or less rounded 

 anterior margin, and pierced by a foramen near its articular border. Some- 

 times the scapula- coracoid Clements are fused at their proximal ends, as 

 in birds. 



The bones of the appendicular skeleton are sometimes very massive, in 

 other cases delicate and hollow ; and the disparity between fore- and hind- 

 quarters is often very considerable, indicating that the presacral region was 

 ordinarily lifted from the ground. The humerus in most cases is inferior in 

 length to the scapula ; the radius and ulna are strongly developed, and 

 always separate. The carpus is often incompletely ossified, and the number 

 of metacarpals is sometimes reduced to three. The digits are short, and 

 the lingual phalanges either hoofed or claw-shaped. 



Many remarkably avian-like characters are to be observed in the pelvic 

 arch and bones of the bind limb, especially among the Predentata. The ilium 

 is depressed and more or less extended antero-posteriorly ; moderately so in 

 the triradiate type of pelvis (Theropoda), very much so in the quadriradiate 

 type (Predentata). The long ischia extend backwards and downwards, and 

 usually join in a median ventral Symphysis. The pre-acetabular process of 

 the ilium (spina iliaca) which serves for the attachment of the pubis, extends 

 further downward than the post-acetabular or ischial process, as in birds. 

 The acetabulum itself is partly open, and the sacrum is partly ornithic, partly 

 reptilian. 



In the Theropoda the pubes are long and slender, and fused in an extended 

 ventral Symphysis. Among the Sauropoda they are shorter, stouter, and 

 broader than the ischia, directed simply downwards and forwards, and united 

 distally in a median cartilaginous Symphysis. In the Predentata (Fig. 326) the 

 pubis is long and broad, but does not join its fellow in the median line in 

 front. At its base, underneath the acetabulum, it gives ofF a long and slender 

 process known as the post-pubis, which is directed downward and backward 

 VOL. II Q 



