412 THE VERTEBRATE SKELETON. 



and triangular, and is wedged in between the other three. It 

 forms about one-sixth of the acetabulum. 



THE POSTERIOR LIMB. 



The posterior limb, like the anterior, is divisible into three 

 parts; these are the thigh, the crus or shin, and the pes. 



The thigh contains only a single bone, the femur. 



The femur is a long straight bone with a nearly smooth 

 shaft and expanded ends. The proximal end bears on its 

 inner side the large rounded head (fig. 79, A, 1) which 

 articulates with the acetabulum. External to the head and 

 divided from it by a deep pit is a large rough outgrowth, 

 the great trochanter (fig. 79, 3). The deep pit is the 

 trochanteric or digital fossa. On the inner side below the 

 head is a smaller roughened surface, the lesser trochanter. 

 The lower or distal end of the bone bears two prominent 

 rounded surfaces, the condyles, which articulate with the 

 tibia. They are separated from one another by the deep 

 intercondylar notch, which is continued above and in front 

 as a shallow groove, lodging a large sesamoid bone, the patella 

 or knee-cap. At the back of the knee-joint are a pair of 

 smaller sesamoids, the fabellae (fig. 79, 7). 



In the young animal there are three epiphyses to the shaft 

 of the femur, one forming the head, one the great trochanter, 

 and one the distal end. 



The crus or shin contains two bones, the tibia and 

 fibula. The tibia is a fairly thick straight bone, expanded 

 at both ends, especially at the head or proximal end. The 

 proximal end is triangular in cross section, and bears two facets 

 for articulation with the condyles of the femur. The anterior 

 surface of the proximal end of the tibia is marked by the 

 strong cnemial crest (fig. 79, 8), which runs some way down 

 the shaft. The distal end of the tibia articulates with the 

 astragalus by an irregular, somewhat square surface. 



