OSTEOLOGY OF CARNIVOROUS DINOSAURS. 



35 



Posterior to the third all of the other cervicals are strongly opisthocoelus. The 

 centra gradually increase in size posteriorly. Viewed from the side (fig. 18) it will 

 be observed that both the anterior and posterior ends of the centra are cut off 

 obliquely to the longer axis of the bone. On the ventral side of the cervicals pos- 

 terior to the third the posterior border takes a decided scoop downward ; but this 

 feature becomes less and less as the base of the neck is approached. 



With the exception of the atlas, all of the cervical vertebrae are strongly cupped 

 on the posterior end of each centrum. On the anterior end there is an almost 

 equally well-developed ball, which is terminated by a rounded, blunt apex that is 

 usually somewhat above the middle. The cervicals in Ceratosaurus differ in having 

 the ball flattened. 



When these vertebrae are articulated the ball does not reach the full depth of 

 the cup, but shows that there was a considerable thickness of cartilage between. 



There is a narrow articular border at the base of the 

 ball, as in Ceratosaurus, that marks to some extent the 

 depth of its insertion into the cup. 



Below the neuro-central sutures the sides of the centra 

 are deeply pinched in, especially toward the front above 

 the capitular facets, at which point there are oval pits, 

 some of which appear to lead into chambers within the 

 centra, these persist as far back as the twelfth vertebra 

 from the skull, in No. 8367. All of the cervicals are 

 highly pneumatic. 



The capitular facets, posterior to those on the axis, 

 are large, placed low down on the side, at the base of 

 the articular ball-like end. In the anterior members of 

 the neck these facets are on stout, heavy buttresses 

 that project straight out from the centrum (fig. 19). 

 Continuing posteriorly the buttresses gradually increase 

 in size and length, and become inclined more and more 

 ventrally as the dorsals are approached. 



In the ninth, one-half of the articulation for the rib 

 is below the level of the median ventral surface of the centrum, whereas in the 

 third vertebra it is wholly above. 



The neurapophyses in all of the cervicals have an extensive attachment to the 

 centrum, spreading out conspicuously at the ends. 



Well-developed diapophyses are present on all vertebrae posterior to the atlas. 

 These are short and comparatively thin dorso-ventrally, but gradually lengthen and 

 become more robust posteriorly. In the anterior cervicals they extend downward, 

 quite close to the side of the centra, but gradually assume a more horizontal position 

 posteriorly until on the ninth vertebra they extend outward at nearly right angles. 

 All are lightened by cavities along the under side, and are supported by thin oblique 

 laminae that extend upward from the anterior and posterior pedicles. 



The articular ends are but little expanded, and the articular surface for the rib 

 looks downward and outward. 



Fig. 19. — Fourth cervical vertebra 

 of Antrodemus valens Leidt cat. 

 NO. 4734, U.S.N.M. J NAT. SIZE. 

 Viewed prom front. <J,diapophysis; 

 p, parapophysis; s, neural spine; z, 

 anterior zygapophysis; z' , pos- 

 terior zygapophysis. 



