268 THE VERTEBRATE SKELETON. 



THE POSTERIOR LIMB. 



This is as usual divisible into three portions, the thigh, 

 the crus or shin, and the pes. 



The thigh is formed by the femur (fig. 48, B, 12), a 

 moderately long stout bone, not unlike the humerus ; it arti- 

 culates with the acetabulum by a fairly prominent rounded 

 head. The distal end articulating with the tibia and fibula 

 is also expanded, and is partially divided into equal parts by 

 anterior and posterior grooves. The flexor surface bears a 

 fairly prominent trochanteric ridge. Each end of the femur 

 is formed by an epiphysis. 



The cms or shin includes two bones, the tibia and 

 fibula. Both are well developed, but the tibia is considerably 

 the larger of the two. 



The tibia (fig. 48, B, 13) is a strong bone with a flattened 

 expanded proximal end articulating with almost the whole of 

 the end of the femur, and a similarly expanded distal end 

 articulating with a bone representing the fused astragalus and 

 centrale. 



The fibula (fig. 48, B, 14) is flattened proximally, and 

 articulates with only quite a small part of the femur, while 

 distally it is more expanded, and articulates with the fibulare 

 (calcaneum) and with a facet on the side of the fused astra- 

 galus and centrale. 



The Pes consists of the tarsus or ankle, and the foot. 



The Tarsus. This, like the carpus, is much reduced and 

 modified from the primitive condition. It consists of only 

 four bones, arranged in two rows of two each. The two 

 bones of the proximal row are much larger than are those of 

 the distal row. The pre-axial of them (fig. 48, B, 15) repre- 

 senting the fused astragalus (tibiale and intermedium) and 

 centrale, articulates proximally with the tibia and fibula, and 

 distally with the first metatarsal, and a small bone representing 

 the first three tarsalia. The post-axial bone, the calcaneum 



