302 OSTEOLOGY OF TUBINARES AND STEGANOPODES. 



Of the pelvis and caudal vertebrae.— The first vertebra that anchyloses 

 with the pelvic sacrum projects entirely beyond the iliac bones (Figs. 

 .".1 ami 32). Its centrum, in common with the next three that follow it, 

 is much compressed from side to side, and its neural spine is continuous 

 with the common neural ridge above of the succeeding segments. 



The firsl five vertebrae that lie beneath the ilia throw out their 

 apophyses in the usual way for their support; the last two of this series 

 meet I lie iliac margins. Here the neural canal and centra are large, so 

 as to afford room for the increase in size of the cord where the sacral 

 plexns is thrown off. 



Twent y-eighth and twenty-ninth vertebra' have their processes thrown 

 directly upward, so that they are not visible upon direct ventral aspect. 



In the thirtieth vertebra they are powerfully developed and extend 

 directly across the basin to abut by anchylosis against the pelvic walls 

 immediately behind the cotyloid cavity on either side. From this point 

 the centra of the uro sacral segments taper quite rapidly in size to an 

 enlarged facet on the posterior aspect of the last one, intended for the 

 first free caudal. 



The extremities of their diapophyses anchylos in a very thorough 

 manner with the inner iliac margins, and a lateral view shows their sides 

 to be riddled with pneumatic foramina between these processes. 



Viewing this pelvis from above, we notice that the entire inner mar- 

 gins of the iliac bones have merged into and completely anchylosed with 

 the sacrum. 



This converts the ilio neural grooves into ilio-neural canals and gives 

 the bone a very compact appearance. 



The anterior margius of the ilia are rounded and are set off with rather 

 a deep and raised emargination. 



Post- and pre-acetabular surfaces are about equal in the extent of 

 their superficial areas. 



The anterior iliac surfaces are concave on either side, and each faces 

 upward and outward to about an equal degree. 



Elevated above these anterior iliac concavities we find the post- 

 acetabular area to be nearly horizontal. Large elliptical foramina are 

 found between the apophyses of the last three or four uro-sacrals, and 

 these latter, likewise, develop quite a prominent neural crest. 



Upon lateral aspect of this pelvis we find a very large cotyloid ring, 

 the inner margin of which is fully equal in size to the outer. A moder- 

 ately sized antitrochanter occupies its usual site, with its articular sur- 

 face directed downward, forward, and outward. 



Behind this occurs an enormous elliptical ischiac foramen, that oc- 

 cupies nearly all of this post-acetabular lateral aspect. Through the 

 fenestra thus formed we are enabled to get a good lateral view of the 

 mo. sacral vertebra' and the extensive pneumatic condition they enjoy 

 (Fig. 31). 



The lower margin of the ilium is sharp and convex; it forms the su- 



