SKELETON AND TEETH 89 



is moulded to fit its head and corresponds in position to the cen- 

 tral of the carpus, but, unlike that carpal, it is a very important 

 element and is never suppressed or lost in any land mammal. 

 The navicular, in turn, rests upon three bones of the second row, 

 which are called respectively the internal, middle and external cu- 

 neiform, which correspond to the trapezium, trapezoid and mag- 

 num of the carpus and to which are attached the three inner met- 

 atarsals, one to each. Finally, the cuboid, the external element 

 of the second row, is a large bone, which supports the calcaneum 

 and often part of the astragalus and to which the fourth and 

 fifth metatarsals are attached ; it is the equivalent of the unci- 

 form in the manus. The number of tarsals is more constant 

 than that of the carpals, but some suppressions and coossi- 

 fications do occur. 



The long bones of the pes constitute the metatarsus, which 

 is the counterpart of the metacarpus. There are never more 

 than five metatarsals in any normal mammal, but there may be 

 any number less than five, down to a single one. In form and 

 size the metatarsals of any given mammal are usually so like 

 the metacarpals, that it requires some experience to distinguish 

 them, but when either manus or pes is especially adapted 

 to some particular kind of work, there may be very decided 

 differences between metatarsals and metacarpals. For example, 

 the burrowing forefoot of the moles is very different from the 

 hind foot, which has undergone but little modification, and 

 even more striking is the difference between the wing of a bat 

 and its foot. Many other instances of a less extreme diver- 

 gence might be enumerated, but when manus and pes are used 

 only for locomotion, as in nearly all hoofed animals and many 

 other mammals, the metacarpals and metatarsals are very 

 similar. When there is a difference in number, it is the general 

 rule that there are fewer metatarsals; an instance of this is 

 found in the tapirs, which have four toes in the front foot and 

 three in the hind. Forms which have a cannon-bone in the 

 manus have it also in the pes, and some, like the peccaries and 



