THE APBNDICULAR SKELETON. 63 



iii. The ischium is the posterior portion of the ventral 

 division and corresponds therefore to the coracoid 

 in the shoulder girdle. It forms the posterior 

 third of the acetabulum. The two ischia are 

 completely fused together in the median plane. 



4. The Hind-Limh. 



The bones have the same general characters as those of the 

 fore-limb, to which tliey correspond very closely. 



a. The thigh. 



i. The femur is a long slender bone, expanded at both 

 ends, and curved slightly in a sigmoid manner. 

 The proximal end or head is spheroidal, and fits 

 into the acetabulum to form the hip joint : the 

 distal end is somewhat expanded laterally. 



h. The leg. 



i. The OS cruris or tibio-fibula is a single bone, rather 

 longer than the femur, slightly curved, and 

 expanded laterally at both ends. It presents 

 along the greater part of its length a groove 

 indicating its correspondence with two bones, 

 tibia and fibula, which in man and many other 

 animals remain distinct from each other. 



C. The ankle, corresponding to the wrist in the fore-limb, 

 consists of two rows of tarsal bones. 



a. The proximal row of tarsal bones consists of two 

 elongated bones united together at both ends, but 

 widely separated in the middle. 



i. The astragalus is on the preaxial or tibial side. 



ii. The calcaneum is on the postaxial or fibular 

 side, and is the larger of the two bones. 



/3. The distal row of tarsal bones consists of two very 

 small bones. 



d. The foot has five complete digits, and a supernumerary 

 toe as well. Each digit consists of a proximal 

 metatarsal bone, beyond which are a variable 

 number of phalanges. 



