DISSECTION OF THE PELVIS. 377 



The bones should be disarticulated to show the articular surfaces. 

 The joint is provided with a rudimentary synovial membrane. 



Sacrococcygeal and Inter-coccygeal Articulations. Ordinarily 

 these are movable joints, the articular surfaces being the opposed 

 extremities of the rudimentary vertebral bodies. These are connected 

 by small intervertebral discs, which are shaped like a biconcave lens, 

 since the bodies of the vertebrae are here convex on both extremities. 



The bones are also invested by a fibrous sheath, which may be 

 supposed to represent the superior and inferior common ligaments 

 of the back and loins. 



Movements. — The biconvex form of the vertebral centra and the 

 suppression of the different processes in this region give a great 

 range and freedom of movement to the tail, which, provided with 

 its appendage of hairs, is admirably fitted to protect the hind quarters 

 of the animal from the attacks of insects. It is interesting to notice 

 the absence of the panniculus carnosus over the area within which 

 the tail is serviceable for this purpose. In animals above middle 

 age it is not uncommon to find the sacro-cocc3 7 geal, and even the 

 first intercoccygeal, joint anchylosed. 



2b 2 



