68 



ANATOMY OF VERTEBRATES. 



56 



their articular surface — upward in the anterior pair, downward 

 in the posterior pair — determines at once the corresponding ex- 

 tremity of a detached sacral vertebra. The thick and strong 

 transverse processes form another characteristic of these vertebne ; 



for a long period the suture 

 near their base remains to show 

 how large a proportion is formed 

 by the pleurapophysis. This 

 element, fig. 55, i, articulates 

 more with the centrum than 

 with the diapophysis developed 

 from the neural arch; it ter- 

 minates by a rough, truncate, ex- 

 panded extremity, which almost 

 or quite joins that of the similarly 

 but more expanded rib, ib. k, 

 of the other sacral vertebra. 

 Against these extremities is ap- 

 plied a supplementary costal 

 piece, serially homologous with 

 the fibrous tract indicated by 

 the dotted lines between h and 

 7, g and 6, fig. 55 ; but ossified, 

 expanded, and interposing it- 

 self between the pleurapophyses 

 and haemapophyses of both sacral 

 vertebra?, not of one only. 

 This intermediate pleurapophy- 

 sial part is called the ' ilium ' 

 fig. 57, 62 : it is short, thick, 

 very broad, and subtriangular, 

 the lower truncated apex form- 

 ino- with the connected extrem- 

 ity of the haemapophysis an arti- 

 cular cavity for the diverging 

 appendage, called the ' hind leg.' 

 The haemapophysis of the anterior sacral vertebra is called t pubis,' 

 fig. 55, 8, fig. 56, 5 ; it is moderately long and slender, but expanded 

 and flattened at its lower extremity, which is directed forward 

 toward that of its fellow, and joined to it through the intermedium 

 of a broad, cartilaginous, haemal spine, ib. 10 and li, completing the 

 haemal canal. The haemapophysis of the second sacral, fig. 55, 9, 

 fig. 56, 4, is broader, subdepressed, and subtriangular, expanding 



Diagram of the hremal arches of the trunk, 

 viewed from above. Crocodile. CC. 



