282 VERTEBRATE ANIMALS. 



brata generally (p. 202). 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 persist- 

 ent of all, and being the only finger left in the Horse. Prop- 

 erly each finger consists of three short bones or phalanges, 

 except the thumb, which has two ; but this rule is occasionally 

 departed from. While the fore-limbs are never wanting, the 

 hind-limbs 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 sub- 

 ject to the same abortion of parts, as we shall see hereafter. 



The great majority of Mammals possess teeth, 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 milk-teeth or deciduous teeth, which is ultimate- 

 ly replaced by a second set, constituting the permanent teeth. 

 No Mammal has ever more 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 incisors, ca- 

 nines, prcemolars, and molars. It is impossible to describe 

 fully which teeth come under each of these heads without en- 

 tering 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. 140). The incisors (i) 

 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 canine or eye-tooth 

 (c) is generally larger or more pointed than the other teeth. 

 The canines are sometimes wanting, or are sometimes present 

 in one jaw and not in the other ; but there are never more 

 than four altogether that is to say, one in each jaw on each 

 side. The prremolars and molars (pm and m) are the so-called 

 " back-teeth," and they vary a good deal in number and function, 



