166 THE STRUCTURE OF THE HORSE. 



fit it for the more important part the hind limb takes 

 in sustaining and propelling the body in walking 

 and running. Several of the vertebrae of this region 

 are united into a solid block, the sacrum, to the sides 

 of which the upper part of each arch or semigirdle 

 is in the closest contact by a large flat surface, and 

 firmly bound by strong ligaments. The arches are, 

 moreover, united to each other in the middle line be- 

 low, without the intervention of anything corre- 

 sponding to a sternum or clavicle. On the outer 

 side of each semigirdle is a deep round cup-shaped 

 depression, the acetabulum, into which the head of 

 the first bone of the limb proper is received, and 

 which therefore corresponds with the glenoid fossa 

 of the shoulder. The joint at this position is the 

 " hip-joint." There is no essential anatomical dif- 

 ference in the construction of the "pelvis," as the 

 whole girdle is called, in man and in the horse, each 

 lateral half being in both originally composed of 

 three distinct bones the ilium, the isclnum, and the 

 pubis which unite before the animal is full grown 

 to form a solid mass, which has received from the 

 old anatomists the curious name of os innominatum. 

 The actual form of the bones presents consider- 

 able differences, the comparatively broad and basin- 

 like pelvis of man relating chiefly to the adaptation 

 of the body to the upright position. 



