THE TEETH IN MAMMALIA. 575 



in the true ant-eaters, or myrmecophaga, amongst the so-called Edentata, 

 there are likewise no teeth. All other Mammalia possess them. 



The number of the teeth in the Mammalia, in conjunction with other differ- 

 ences in shape or kind, furnishes an important means of zoological distinction. 

 It ranges from 2 in the narwhal, to as many as 190 in the dolphins. In the 

 elephant, there are at most 10, usually only 6, viz., one entire molar, or 

 sometimes parts of two, on each side of both jaws, together with the two 

 tusks of the upper jaw. In the Eodents, the ordinary number is 20, but there 

 are sometimes only 12, and in the hare and rabbit 28. In the Ruminants, in 

 the apes of the Old World, and commonly throughout the Mammalia, as in 

 Man, there are 32, but 44 is said to be the typical number. (Owen.) In one 

 of the armadilloes, as an exception to the rule in that genus, there are 98 teeth. 

 Amongst the Cetacea, the narwhal, just mentioned, and some other species, 

 have only 2 teeth ; the cachalot has more than 60, the common porpoise between 

 80 and 90, and the true dolphins from 100 to 190. 



The/orm of the teeth presents greater variety in the Mammalia than in any 

 other Class. When numerous, they are usually prehensile, small, pointed, 

 and of nearly equal size throughout the jaw ; sometimes slightly recurved, and 

 sometimes variously flattened or compressed. When the teeth are in moderate 

 number, some are devoted to one purpose and some to another, and they are 

 usually modified into incisor, canine, premolar, and molar teeth. The incisors, 

 as in Man, are flat, chisel-shaped, and cutting or gnawing ; the canines are 

 larger and conical, to bite, hold, and tear ; the premolars and molars are va- 

 riously cusped or tuberculated, and either flattened at the sides for cutting, or 

 broad^at the summit for grinding the food. The incisor teeth are smallest in 

 the insectivorous, larger in the carnivorous and frugivorous species, of great 

 strength in the cropping Herbivora, but especially strong in the gnawing Ro- 

 dentia. The canine teeth, prominent in the carnivorous dogs and cats, are 

 also large in many non-carnivorous animals, as the ape, boar, musk-deer, ele- 

 phant, and others, in which they are used for offence or defence. The carniv- 

 orous molars are generally flat, narrow, ridged, and tuberculated, the anterior 

 ones being often very diminutive. The herbivorous molars are flat-crowned, 

 quadrangular, or lozenge-shaped, and provided with tubercles, as in the Quad- 

 rumana, or marked with crescentic or transverse ridges and furrows, as in the 

 Ruminants, Solipeds, Pachydermata, and Rodents. In animals living on 

 mixed diet, the crowns of the molar teeth are furnished with blunt tubercles. 

 The tusks of the elephant are huge canine teeth ; those of the walrus are also 

 canine. The single tusk of the male narwhal or Monodon, several feet in 

 length, is also an upper canine tooth ; it springs on one side of the median line, 

 from the superior maxillary bone ; but an immature tooth is found concealed 

 in the bone of the opposite side ; in the female narwhal, both tusks remain un- 

 developed, one in each upper jaw-bone. The curved canine tusks of the Baby- 

 roussa are also remarkable ; those of the upper jaw are larger and longer than 

 those of the lower jaw, and sometimes perforate the upper lips. 



The teeth in Mammalia are limited to the jaws. They are confined to the 

 inferior maxilla in the cachalot, to the premaxillary bones in the upper 

 jaw in the narwhal, and to the superior and inferior maxillary bones, being 

 wanting in the premaxillary bones, in most Ruminants. But usually, teeth 

 are found in all three of these bones. However varied in number and in form, 

 mammalian teeth are always arranged, in each jaw, in a single row or dental 

 arch, in which, where different kinds of teeth exist, one or more gaps occur, 

 named diastemata. When a diastemata is absent, the teeth are of equal length. 

 In the human jaw, as already mentioned, there is no diastema, but this is 

 also the case in certain extinct quadrupeds. 



The mammalian teeth are usually fitted closely into sockets in the jaws, each 

 tooth and each fang, if these be multiple, having its own socket, lined by a 

 periosteum which fixes it. In certain Cetacea, the sockets are wide and shal- 

 low, and the teeth are attached to the gum, rather than fixed in the jaw. Each 

 tooth generally has a constricted part or neck, between the crown and fang, to 

 which the gum is fixed ; but no neck is seen in the numerous small teeth of 

 the dolphin, in the tusks of the narwhal, elephant, and walrus, or in the in- 

 cisors of the Rodentia. 



The teeth of most Mammalia, like those of Man, consist chiefly of dentine, 



