102 VEKTEBRiE OF THE CROCODILE. 



haemal arch; it is termed "iscliium." The great develop- 

 ment of all the elements of these hasmal arches, and the 

 peculiar and distinctive forms of those that have thereby 

 acquired, from the earliest dawn of anatomical science, 

 special names, relates physiologically to the functions of 

 the diverging appendage which is developed into a potent 

 locomotive member. This limb appertains properly, as 

 the proportion contributed by the ischium to the articular 

 socket and the greater breadth of the pleurapophysis sliow, 

 to the second sacral vertebra ; to which the ilium chiefly 

 belongs. 



The first caudal vertebra, which presents a ball for 

 articulating with a cup on the back part of the last sacral, 

 retains, nevertheless, the typical position of the ball on 

 the back part of the centrum ; it is thus biconvex, and 

 the only vertebra of the series which presents that 

 structure. 



The first caudal vertebra, moreover, is distinguished 

 from^the rest by having no articular surfaces for the hge- 

 mapophyses, which in the succeeding caudals form a 

 haemal arch, like the neurapophyses above, by articulat- 

 ing directly with the centrum. The arch so formed has 

 its base not applied over the middle of a single centrum, 

 but, like the neural arch in the back of the tortoise and 

 sacrum of the bird, across the interspace between two 

 centrums. The first haemal arch of the tail belongs, how- 

 ever, to the second caudal vertebra, but it is displaced a 

 little backwards from its typical position. 



The caudal haemapophyses, A A, coalesce at their lower 

 or distal ends, from which a spinous process is prolonged 

 downwards and backwards ; this grows shorter towards 

 the end of the tail, but is compressed and somewhat ex- 

 panded antero-posteriorly. The haemal arch so constituted 

 has received the name of "chevron bone." 



