372 THE ANATOMY OF THE HORSE 



tliere is posteriorly an articular surface of an oval form, and on the sixth 

 there is a similar one on each surface, the posterior being slightly concave, 

 and fitting to a corresponding facette on the sacrum. 



THE SACRUM 



This bone, in form irregularly prismatic, is made up from the conjunc- 

 tion by ossification of five vertebrae, in which latter condition it is found 

 in the embryo. It is united in front with the last lumbar vertebra by 

 three articulatory surfaces (^, ^, o. Fig. 1 9) posteriorly with the first bone 



Fio. 19.— The SAcnrM. 



1. Fore view of the sacrum. 



2. 2. 2. etc. Spinous i>roi't>sse.s. 



3. I.jiteral free siirf;i<o. 



4. Head articulating witli the concavity on the 



head oJ the last lumbar vertebra. 

 .I. .'i. Oblique processes. 



(■'. t). Surfaces articulating with transverse pro- 

 cesses of last lumbar vertebra. 



7. 7. 7. etc. Foramina for the passage of the inferior 

 sacral nerves. 



S. 8. Surfaces articulating with the ilium. 



of the coccyx, and on each side with the ilium or hip-bone, by a large 

 rough surface (g, g Fig. 1 9). The whole bone is slightly curved, with its 

 concavity downwards. This inferior surface is broad and smooth, forming 

 the superior boundary of the pelvic basin. On it are plainly traced four 

 transverse lines, marking the situation of the original divisions into separata 

 bones. Here are also four large holes on each side for the passage of the 

 inferior sacral nerves. The superior surface is furnished with five spines 

 (o o 2, 2 Fig. 19), corresponding to the spinous processes of the luir.l)ar 

 vertebra\ They unite at their bases, but are distinct above, terminating 

 in a protuberance which is sometimes bifid. The two sides are thick and 

 concave in the middle, and terminate posteriorly in a rough lip. Ante- 

 riorly they form an irregular surface, having an inclination from above 

 downwards, backwards, and inwards. The inferior portion of this face is 

 lined with cartilage, which is attached both to it and to the ilium, while 



