280 MAMMALIA. 



ally as not forming parts of the skeleton properly so called, 

 but as being ossifications of the internal tendons of the 

 "external oblique" muscles of the abdomen (fig. 598). 



In those Mammals which jDossess hind-limbs, the normal 

 composition of the member is of the following parts : 1. A 

 thigh-bone or femur; 2. Two bones forming the shank, and 

 known as the tibia and fibula ; 3. A number of small bones 

 constituting the ankle or tarsus ; 4. The " root " of the foot, 

 made up of the "metatarsus;" 5. The phalanges of the toes 

 (see fig. 483). 



The thigh-bone or femur articulates with the pelvis, usu- 

 ally at a very open angle. In Man it is distinguished by 

 being the longest bone of the body, and by having the axis 

 of its shaft nearly parallel to that of the vertebral column. 

 In most Mammals the femur is relatively shorter, and the 

 axis of its shaft deviates considerably from that of the 

 spine, being sometimes at right angles, or even at an acute 

 angle. 



Of the bones of the leg proper the tibia corresponds to the 

 radius in the fore-limb, as shown by its carrying the tarsus ; 

 and the fibula is the representative of the ulna. The articu- 

 lation between the tibia and fibula on the one hand, and the 

 femur on the other, constitutes the " knee-joint," which is 

 usually defended in front by the " knee-pan " or patella, a 

 large sesamoid bone developed in the tendons of the great 

 extensor muscles of the thigh. The patella is of small size 

 in the Camivora, but does not appear to be wanting in any 

 except the Marsupials. In many cases the tibia and fibula 

 are anchylosed towards their distal extremities. In the 

 Horse the fibula has much the same character as in Birds, 

 being a long splint-like bone which only extends about half- 

 way down the tibia. In the Euminants the reverse of this 

 obtains, the upper half of the fibula being absent, and only 

 the lower half present. 



The tibia articulates with the tarsus, consisting in Man 

 of seven bones, but varying in different Mammals from four 

 to nine. 



The foot consists normally of five toes connected with the 

 tarsus by means of five metatarsal bones, which closely re- 



