GENERAL CHARACTERISTICS. 
9 
the astragalus or ankle-bone, are sjoecially modified. In the foot proper the 
bones correspond with those of the hand; those representing the metacarpals being ) 
however, termed metatarsals. It will fre¬ 
quently be found convenient to speak of the 
extremity of the fore-limb, or hand, as the 
manus; 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 known 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 jaws 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 
