I 



■LECTURE III. 135 



in eqiiilibrio on the bone which supports 

 the base of the vertebral column. This 

 wedge-shaped bone is called the os sacrum, 

 they say, because that part of the animal 

 was frequently offered in sacrifices. It is very 

 broad above and narrrow below, so that the 

 weight which it supports would only tend 

 to depress the broader part of the wedge in- 

 to the narrower space, and render the fabric 

 more secure. The sacrum is convex be- 

 hind, and concave in front, for it forms a 

 part of a somewhat circular bony cavity 

 placed at the bottom of the belly and 

 called the pelvis or basin. The sacrum 

 terminates by a smooth surface of small 

 extent, and oblong in the lateral direction, 

 on which there moves backwards and for- 

 wards a little bone which is called the os 

 coccygis, from its supposed resemblance to 

 a cuckow's beak. This bone is occasionally 

 thrust backwards, but is usually held for- 

 wards by muscles connected to it, and af- 

 fords the last bony support for the weight 

 of those bowels which may gravitate into 

 the cavity of the pelvis in particular posi- 

 tions of the body. 



K 4 



