GENERAL CHARACTERISTICS. 



the astragalus or ankle-bone, are specially modified. In the foot proper the 

 bones correspond with those of the hand ; those representing the metacarpals being, 

 however, termed inrtatarsals. It will fre- 

 quently be found convenient to speak of the 

 extremity of the fore-limb, or hand, as the 

 iiHiini.s; while the hind foot may be termed 

 the pes. 



In the foregoing summary we have spoken 

 of the hand and foot as consisting of five 

 fingers and toes, or digits ; and this is the case 

 with most Monkeys, many Carnivores, Rodents, 

 etc. In other cases, however, and especially 

 among the Hoofed Mammals or Ungulates, 

 there is a tendency to the reduction of the 

 number of digits. Thus in the cattle and deer, 

 commonly kno\vn as Ruminants, the number 

 of functional digits is reduced to two, corre- 

 sponding to the third and fourth of the typical 

 series of five ; while in the horse only a single 

 digit remains, which in the fore-limb corre- 

 sponds to the middle or third finger of the 

 human hand, and in the hind -limb to the 

 middle toe. 



Arrangement of Almost all Mammals when 

 the Teeth, adult have both jaw r s provided 

 with a series of teeth, varying greatly in number 

 and structure in the different groups. These 

 teeth are almost invariably fixed in separate 

 sockets ; and while the front teeth have but a 

 single root or fang, the side or cheek-teeth 

 very generally have two or more such roots, 

 each of which occupies a separate division of 

 the socket. In all cases the teeth are fixed in 

 their sockets merely by the aid of soft tissues 

 connected with the gum, and are never welded 

 to the jaws by a deposit of bone. Very gener- 

 ally there is a sharply-marked line of division, termed the neck, between the root, 

 or portion of the tooth implanted in the jaw, and the crown or exposed portion. 



In most of those Mammals, in which the teeth of different parts of the jaw 

 differ in structure from one another, there are two distinct sets of teeth developed 

 during life. The first of the two includes the milk- or baby-teeth, which are 

 generally shed at a comparatively early age, are of small size and few in number, 

 and are finally succeeded by the larger and more numerous permanent set, which 

 remain during the rest of life, unless previously worn. 



In those Mammals in which the permanent teeth differ from one another in 

 form in different regions of the jaw, we are enabled from their position, and also 



HUMAN SKELETON. 



