CHAPTER XVII. 



THE PELVIC GIRDLE. 



THE posterior limb consists of a pelvic girdle and three 

 segments belonging to the limb proper, viz. the thigh, the 

 leg, and the foot, or pes. 



The PELVIC GIRDLE is present in some form in all Mam- 

 mals, though in the Cetacea and the Sirenia it is in an 

 exceedingly rudimentary condition. 



In all Mammals, except those belonging to the two 

 orders just named, each lateral half of the pelvic girdle 

 consists primitively, like the corresponding part of the an- 

 terior limb, of a rod of cartilage crossing the long axis of 

 the trunk, having an upper or dorsal, and a lower or ventral, 

 end. The upper end diverges from that of the opposite 

 side, but the lower end approaches, and, in most cases, 

 meets it, forming a symphysis^ without the intervention of 

 any bone corresponding to the sternum. 



The pelvic girdle differs from the shoulder girdle in being 

 articulated to the vertebral column, at a point near to, but 

 not at, the upper end of the rod. 



Like the shoulder girdle, it bears on its outer side, near 

 the middle, a cup-shaped articular cavity (acetabitlum or 

 cotyloid cavity, Fig. 113, a, p. 313), into which the proximal 

 extremity of the first bone of the limb proper is received. 



