CRYPTODONTIA. 265 



Rhynchosaurus, excepting their biconcave structure, resemble 

 the vertebrae of most recent lizards. In the modification next 

 to be noticed, they shew one of the vertebral characters of the 

 Dinosauria. A broad obtuse ridge rises from the upper con- 

 vex surface of the posterior zygapophysis, and arches forwards 

 along the neural arch to the anterior one ; the upper part of 

 this arched angular ridge forms, with that of the opposite side, a 

 platform, from the middle line of which the spinous process is 

 developed. Nothing of this kind is present in existing lizards. 

 The base of the spinous process is broadest behind, and com- 

 mences there by two roots or ridges, one from the upper and 

 back part of each posterior zygapophysis ; the height of the 

 spine does not exceed the antero-posterior diameter of its 

 base ; it is obliquely rounded off. The spinal canal sinks into 

 the middle part of the centrum and rises to the base of the 

 spine, so that its vertical diameter is twice as great at the 

 middle as at the two extremities ; this modification resembles 

 in a certain degree that of the vertebras of the Palceosaurus 

 from the Bristol conglomerate. 



The skull (fig. 91, a) presents the form of a four-sided 

 pyramid, compressed laterally, and with the upper facet arch- 

 ing down to the apex, which is formed by the termination of 

 the premaxillaries, aa. The very narrow cranium, wide tem- 

 poral fossa?, on each side, bounded posteriorly by the parietal 

 and the mastoid bones and laterally by strong compressed 

 zygomata, the long tympanic pedicle (ib. r) descending verti- 

 cally, and terminating in a convex pulley for the articular con- 

 cavity of the lower jaw, the large and complete orbits (g), and 

 the short, compressed, and bent down upper jaw, are lacertian 

 characters. The lateral compression and the depth of the 

 skull, the great vertical breadth of the upper, and the vertical 

 breadth of the lower, jaw-bones, shew that it is not a batra- 

 chian. The shortness of the muzzle, and its compressed form, 

 remove it from the Crocodilians. No Chelonian has the 



