VERTEBRATA: MAMMALIA. 647 



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

 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 some- 

 times at right angles, or even at an acute angle. 



Of the bones of the leg proper (crus) 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 articula- 

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

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

 ally 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 Car- 

 nivora^ but does not appear to be wanting in any except in 

 some of 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 Ruminants 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, or pes, consists normally of five toes, connected 

 with the tarsus by means of five metatarsal bones, which closely 

 resemble the metacarpals. In the Ruminants there are two 

 principal metatarsals, and these are anchylosed in the adult, 

 and carry two toes. In the Horse there is only one complete 

 metatarsal supporting a single toe. As a rule, the number of 

 digits in the hind-limb or foot is the same as that in the fore- 

 limb or hand ; but this is not always the case. In the Lions, 

 Tigers, Cats, and Dogs, the posterior limb carries only four 

 toes, the innermost toe or hallux being wanting. In the Quad- 

 rumana, again, all the five toes are generally present, but the 

 four outer toes are much longer than in Man, and the hallux 

 is shorter than the other toes, and often opposable to them, so 

 that the foot forms a kind of posterior hand. The hallux is 

 also not uncommonly opposable in other cases. 



The cranial bones are invariably connected with one another 

 by sutures, and in no other examples than the Monotremes 

 are these sutures obliterated in the adult. The differences of 

 opinion which are entertained as to the fundamental structure 



