THE HIND-LIMB 291 



obturator foramen. It forms about a third 

 of the acetabulum, behind which it bears 

 on its inner surface the sharp, backwardly 

 directed ischial spine. Its posterior part is 

 flattened, the margin being thickened to form 

 the ischial tuberosity, which is raised on its 

 outer surface into a prominent hooked pro- 

 cess. The ischium corresponds to the coracoid 

 in the shoulder-girdle. 



iii. The pnbes, which is the smallest bone of the 

 three, forms a very small portion of the 

 acetabulum, where it is separated by a notch 

 from the ischium. It unites along its ventral 

 border with its fellow of the opposite side 

 to form the anterior part of the symphysis, 

 the hinder portion of which is formed by 

 the ischium : the line of union between these 

 two bones is visible only in very young 

 skeletons. 



D. The Hind-Limb. 



The hind-Hmb is much larger than the fore-limb, and hke 

 this is divisible into four main portions. 



In the hind-limb the departure from the primitive condition 

 is much less marked than in the fore-limb. The whole limb 

 has rotated forwards through about a right angle, so that the 

 preaxial border is directed inwards, and the postaxial out- 

 wards ; the original dorsal surface being turned forwards, and 

 the ventral surface backwards. 



1. The thigh, like the arm, contains a single bone, the 

 femur. Certain sesamoid bones in connection with 

 the knee-joint may be considered with it. 



i. The femur is an elongated bone, consisting of a 

 cylindrical shaft, bent slightly forwards, and 

 two enlarged extremities. 



The proxinjal end bears on its inner or 

 preaxial side the prominent rounded head , 



u2 



