566 CLASS XVIT. 



lower extremity the outer ankle (malleolus externus]. The first 

 tarsal bone (talus s. astragalus] is connected by a hinge-joint 

 with the tibia and is placed between the inner and outer ankles. 

 Below, the astragalus is connected with the heel-bone (calcaneus), 

 to the projecting posterior extremity of which the tendon of Achilles 

 is affixed. These two are the principal bones of the root of the 

 foot (tarsus), besides which in the human skeleton there are five 

 other bones, so that the tarsus consists of seven bones in all, whilst 

 in the other mammals the number of bones in this part of the foot 

 varies from four to nine. In the pachyderms, the carnivorous and 

 the quadrumanous animals, there are on the whole seven bones in 

 the root of the foot as in man. On the other hand, the tarsal bones 

 are more numerous in the edentate mammals and in many rodents. 

 In the horse there are two cuneiform bones instead of three; the other 

 bones are the same as in man, and the entire number is thus six. 

 So also is it in the camel, but the rest of the ruminants have only 

 five tarsal bones, since in them the navicular bone has coalesced with 

 the cubiform bone ; and the giraffe has only four, for with a similar 

 coalescence of these two bones, only one cuneiform bone is present. 

 In Otolicnus and Tarsius, long-footed Lemurids, the navicular bone 

 is very long and lies by the side of the heel-bone, also lengthened, 

 in the same manner as in the fore-arm the radius lies by the side 

 of the ulna. Two such long tarsal bones, placed side by side, 

 occur also amongst the reptiles in the frogs. 



The fore-foot (metatarsus] usually counts as many bones as there 

 are toes present. The metatarsus in the ruminant and solidungu- 

 late animals is conformable to the metacarpus (comp. above, p. 562). 

 In the genus Dipus amongst the rodents the three middle meta- 

 tarsal bones coalesce to form a single bone, which terminates below 

 in three processes, to which the three large toes are connected, and 

 which thus resembles the principal bone of the root of the foot in 

 birds (see above, p. 332). fc 



The digits of the foot in the ruminants, the solidungulates, and 

 commonly also in the pachyderms, correspond in number and form 

 to those of the hand. Such also is the case in most of the carnivo- 

 rous animals ; although in the genus Felis and Cam's the thumb 

 (hallux) of the hind-foot is not developed, of which a trace only is 

 observed in the fore-foot. In the monkeys the thumb is shorter, 

 but the other digits are longer than in the human foot. 



