10 FOSSIL REPTILIA OF THE 



The lateral compression of the centrum increases in the sixth ( 8 ) and seventh 

 ( 9 ) (conspicuous) vertebrae, in which the under surface forms an obtuse ridge ; 

 in the eighth vertebra (10) this surface is broader and more rounded. In none of 

 these vertebras is a process developed from the under surface, as in the hinder cervical 

 and anterior dorsal vertebrae of the Crocodiles ; and in none of them is the anterior 

 articular surface of the centrum convex, as in the Streptospondylus. 



The most striking character of the vertebrae of the Hylaeosaurus is the great 

 development of the neural arch and its processes. The anterior articular processes 

 extend (in the anterior dorsal and cervical vertebrae) over half the centrum next in 

 front, and a broad diapophysis (upper transverse process) is developed from the side 

 of the neurapophysis and along its anterior continuation : the diapophysis extends 

 horizontally outwards, is notched anteriorly, and contracts to an obtuse point, against 

 which the tubercle of the rib articulates : it is flat transversely, slightly concave length- 

 wise, and smooth below. The diapophyses increase in length and strength as the 

 vertebrae extend along the trunk ; and the ribs, which they contribute to support, 

 exhibit a still more rapid increase. The ribs present, as in the other Dinosaurs and 

 Crocodiles, a bifurcated vertebral end, for the double articulation above described 

 (T. IV, pi 3, and the ribs attached to 9 and 10). The rib {pi 2) which appears to 

 be the second, and belongs to the cervical region, is short and pointed, not exceeding 

 4 inches in length. The neck and head of the rib corresponding with the seventh 

 conspicuous vertebra, apparently the third free rib {pi 3), is 2 inches 2 lines in length ; 

 the tubercle, or upper head, is 10 lines long; the breadth of the rib at the point of 

 bifurcation is 1 inch 1 line ; the entire length of this rib is 5^ inches. The neck of the 

 fourth rib {pi 4) has the same length as that of the third, but is twice as thick and 

 strong ; the tubercle is broader but shorter. Beyond the tubercle the shaft of the rib 

 is bent at nearly right angles with the neck. This soon begins to shorten, and the 

 shaft of the rib to lengthen, until it becomes attached solely to the diapophysis. 



In the dorsal vertebrae the body increases in all its proportions, excepting its 

 length. The lateral compression now manifests itself at the upper part of the centrum, 

 just below the neurapophysial suture ; the under surface of the posterior dorsal and 

 lumbar vertebrae is convex transversely, but in a less degree than in the Megalosaurus, 

 and in some it is obscurely carinated. The external surface at the middle contracted 

 part of the vertebra is moderately smooth, but the minute striae give it a somewhat 

 silky lustre ; it is longitudinally but irregularly ridged and grooved near the articular 

 ends. These are both slightly concave at the centre, more slightly convex near the 

 circumference. 



The difference between the vertebrae of the Hylaeosaur and the biconcave Croco- 

 dilian vertebrae is chiefly manifested in the development of the neural arch. The 

 modification of this part in the cervical vertebrae has already been mentioned. In the 

 dorsal vertebrae (T. VIII, fig. 10) each neurapophysis rises vertically, contracting in 



