308 VERTEBRATE ANIMALS. 
As regards the structure of the fore-limbs (fig. 118), the general 
plan of conformation is the same as described in treating of the 
Vertebrata generally (p. 220). The shoulder-blade or scapula 
is never absent ; and the coracoid bone, which is so marked a 
feature in the birds, is with hardly an exception amalgamated 
with the scapula. The clavicles or collar-bones are often want- 
ing or rudimentary, but in no Mammal are they ever united 
together in front so as to form a merry-thought or “ furculum.” 
The regular number of fingers is five, but they vary from one to 
five, the middle finger being the longest and most persistent of 
all, and being the only finger left in the Horse. Properly each 
finger consists of three short bones or phalanges, except the 
thumb, which has two; but this rule is occasionally departed 
from. Whilst the fore-limbs are never wanting, the hind-lmbs 
are sometimes absent, as in the Whales. Generally speaking, 
however, the posterior limbs are present, and the pelvic arch 
has much the same structure as in man. The foot—like the 
hand—consists regularly of five digits, but it is subject to the 
same abortion of parts, as we shall see hereafter, 
The great majority of Mammals possess Zeezh, but these are 
only present in the embryo of the whalebone Whales, and are 
altogether wanting in the scaly and great Ant-eaters. The 
teeth are also almost invariably implanted in distinct sockets in 
the jaw. Some Mammals have only a single set of teeth ; but 
in most cases the young Mammal possesses a set of what are 
called the zzz/k-teeth or deciduous teeth, which is ultimately 
replaced by asecond set, constituting the Jermanent teeth. No 
Mammal has ever ove than two sets of teeth. In man, and in 
many other Mammals, the teeth are divisible into four groups, 
which differ from one another in position, appearance, and 
function. ‘These are termed respectively the zuzczsors, canines, 
premolars, and molars. It is impossible to describe fully 
which teeth come under each of these heads without entering 
into unnecessary details as to the structure of the jaws. It 
must be sufficient here to point out the general characters and 
position of these groups in a good illustrative example, such as 
one of the higher Apes (fig. 168). The incisors (2) vary greatly 
in size and number, but they are always placed in the front of 
the mouth, and are the teeth which are used in simply biting 
or dividing the food. The canzne or eyetooth (c) is generally 
larger and more pointed than the other teeth. The canines are 
