PROFESSOR OWEN, ON THE RHYNCHOSAURUS. 357 



each angle of its base a broad triangular process with a flat articular 

 surface; the two anterior surfaces look directly upwards, the posterior 

 ones downwards ; the latter are continued backwards beyond the posterior 

 extremity of the centrum; the tubercle for the simple articulation of 

 the rib is situated immediately beneath the anterior oblique process. So 

 far the vertebra? of the Rhynchosaurun, always excepting their biconcave 

 structure, resemble the vertebra of most recent lizards. In the modifica- 

 tion next to be noticed, they show one of the A*ertebral characters of the 

 Dinosauria*. A broad obtuse ridge rises from the upper convex surface 

 of the posterior articular process, and arches forwards along the neur- 

 apophysisf above the anterior articular process, and gradually subsides an- 

 terior to its base: 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. This structure is not present in existing 

 lizards; the sides of the neural arch in their vertebras immediately 

 converge from the articular processes to the base of the spine, without 

 the intervention of an angular ridge formed by the side of a raised 

 platform. The base of the spinous process in the Rhynchosaur is broadest 

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

 and back part of each posterior articular process : they meet at the 

 posterior part of the summit of the neural arch, whence the spinous 

 process is continued upwards as a simple plate of bone, its base extend- 

 ing forwards along about two thirds of the length of the platform, 

 which then again divides into two ridges which diverge from each other 

 in slight curves to the anterior and external angles of the neurapo 

 physes. The interspace of the diverging anterior crura of the base of 

 the spine is occupied by a triangular fossa, not continued into the sub- 

 stance of the spine; this fossa is bounded below by a horizontal plate 

 of bone extended over the anterior part of the spinal canal, and ter- 

 minated by a convex outline. The anterior margin of the spinous 



* The characters of this extinct Order of Reptiles are given in the Report of the British 

 Association, 1841, p. 102. 



t The vertebral nomenclature, which I have been compelled to invent -for the requisite 

 clearness and brevity of description of these most complicated and most common of Reptilian 

 fossils, is explained in the Geological Transactions, Vol. V, pt. iii, Second Series, p. 518. 

 Vol. VII. Part III. Rg 



