646 



PEOF. H. G. SEELEY 0~N THE REPTILE 



of Biinzel's figure of this vertebra is the centrum ; the transverse 

 process is lettered d. 



Caudal Vertebral. 



(See Mnzel, pi. ii. figs. 4-8, pi. iv. figs. 6-9, pi. viii. figs. 1, 7, 8, 16.) 



There are eighteen caudal vertebras preserved. The earlier ones have 

 strong transverse processes, which, however, are more or less broken 

 away, are compressed from above downward, and appear to have been 

 short ; and the vertebras differ from each other in passing backward in 

 the suppression of these transverse processes, which become represented 

 by sharp ridges in the middle part of the series, while towards the end 

 of the tail all trace of their existence is lost, and the centrum, which 

 hasbecome gradually reduced in vertical and transverse measurements, 

 assumes a constricted or dicebox-like outline. None of the caudal 

 vertebras, except the earliest, appear to have possessed a prominent 

 neural spine ; for the neural arch has well-developed zygapophyses 

 and a concave outline from front to back. The arch, however, soon 

 becomes reduced in size, and in the middle of the series is greatly 

 compressed from side to side, and the articular zygapophysial facets 

 are lost, while towards the end of the tail the neural arch is a mere 

 rudiment. The chevron bones were at first apparently large, and arti- 

 culated with large oblique facets at the hinder margin of the base of 

 the centrum ; but these facets do not appear to have been quite distinct 

 from each other, though they were partly divided by the median groove 

 on the base of the centrum. They soon become relatively small, and 

 near the end of the tail are quite separated from each other, though 

 (it may be by an injury received during life) they appear to have become 

 united to the centrum. Two of the hinder caudal vertebras are 

 fractured through the centrum, and show the bones to have contained 

 central hollow spaces, which, however, were not clearly defined by a 

 smooth bony lining, but are rather like the medullary cavities of the 

 long bones of mammals. The articular edges, where preserved, are at 

 first somewnat rounded, but terminate in a sharp outer margin. 

 They are very slightly concave, and later on in the series become 

 almost flat, showing that the tail possessed but little flexibility. 



The earliest vertebra preserved has the centrum leaning slightly 

 forward. It is fully ly 7 ^ inch long, and the same depth to the 

 chevron facets on the hinder basal margin, which, however, is badly 

 preserved. The width of the centrum in front, at the base of the 

 transverse processes, is 1^ inch. The corresponding width behind 

 is a trifle less. The anterior articular face is nearly flat, but had 

 the margin rounded. The posterior articular face is more concave, 

 and the rounding of the margin is less marked. The upper borders 

 of the transverse processes are on a level with the base of the 

 neural canal. They are placed nearer to the anterior than to the 

 posterior articular face, are transversely oblong where broken close 

 to the centrum, and measure T 8 ^ inch in length, ju i n depth. Be- 

 low them the centrum is compressed ; the base is broad, ill defined, 

 1 inch in width, rounds into the sides, and is divided longitudinally 

 by a shallow groove about inch in width, which is most marked 



