14 FOSSIL REPTILIA OF THE LONDON CLAY. 



a Gavial I have seen thirteen dorsal and two lumbar ; in that of a Crocodihis cata- 

 phractus twelve dorsal and three lumbar ; in those of a Crocodihis acatus, and Alligator 

 lucius, eleven dorsal and four lumbar, and this is the most common number ; but in 

 the skeleton of the Crocodile, I believe of the species called Croc, biporcatus, described 

 by Cuvier,* he gives five as the number of the lumbar vertebras. But these varieties 

 in the development or coalescence of the stunted pleurapophysis are of little essential 

 moment ; and only serve to show the artificial character of the ' dorsal' and ' lumbar' 

 vertebrae. The coalescence of the rib with the diapophysis obliterates of course the 

 character of the ' costal articular surfaces ;' which we have seen to be common to 

 both dorsal and cervical vertebras. The lumbar zygapophyses have their articular 

 surfaces almost horizontal, and the diapophyses, if not longer, have their antero-posterior 

 extent somewhat increased ; they are much depressed, or flattened horizontally. 



The sacral vertebrae are very distinctly marked by the flatness of the coadapted 

 ends of their centrums : there are never more than two such vertebras in the Crocodilia 

 recent or extinct ; in the first the anterior surface of the centrum is concave, in the 

 second it is the posterior surface ; the zygapophyses are not obliterated in either of 

 these sacral vertebras, so that the aspects of their articular surface — upwards in the 

 anterior pair, downwards in the posterior pair — determines at once the corresponding 

 extremity of a detached sacral vertebra. The thick and strong transverse processes 

 form another characteristic of these vertebras ; for a long period the suture near their 

 base remains to show how large a proportion is formed by the pleurapophysis. This 

 element articulates more with the centrum than with the diapophysis developed from 

 the neural arch ; f it terminates by a rough, truncate, expanded extremity, which almost 

 or quite joins that of the similarly but more expanded rib of the other sacral vertebrae. 

 Against these extremities is applied a supplementary costal piece, serially homologous 

 with the superadded piece to the proper pleurapophysis in the dorsal vertebras (li , fig. 6, 

 p. 5, Part I), but here interposing itself between the pleurapophyses and hasmapophyses 

 of both sacral vertebras, not of one only. This intermediate pleurapophysial piece is 

 called the ' ilium ;' it is short, thick, very broad, and subtriangular, the lower truncated 

 apex forming with the connected extremities of the hasmapophysis an articular cavity for 

 the diverging appendage, called the ' hind leg.' The hasmapophysis of the anterior 

 sacral vertebra is called ' pubis :' it is moderately long and slender, but expanded 

 and flattened at its lower extremity, which is directed forwards towards that of its 

 fellow, and joined to it through the intermedium of a broad, cartilaginous, hasmal spine, 

 completing the hasmal canal. The posterior hasmapophysis is broader, subdepressed, 

 and subtriangular, expanding as it approaches its fellow to complete the second hasmal 



* Tom. cit., p. 95. It is to be observed that Cuvier begins to count the dorsal vertebra when the rib has 

 changed its hatchet-shape for a styloid shape. 



t Cuvier, who well describes this structure, remarks, "aussi meritent-elles plutot le nom des cotes que 

 celui d' apophyses transverses." (Tom. cit., p. 98.) 



