898 1 



in the system of Linnaeus a small fraction 

 his genus LACERTA. 



TEETH. 



of 



Dental System of Mammals. 



The class Mammalia, like that of Beptllia 

 and Pisces, includes a few genera and species 

 that are devoid of teeth : the true ant-eaters 

 (Myrmecophaga), the scaly ant-eaters or Pan- 

 golins (Mams), and the spiny monotrematous 

 ant-eater (Echidna), are examples of strictly 

 edentulous Mammals. The Ornithorhynchus 

 has horny teeth, and the whales (Eakcna and 

 Balcenopterd) have transitory embryonic cal- 

 cined teeth*, succeeded by whalebone sub- 

 stitutesf in the upper jaw. Horny processes 

 analogous to, perhaps homologous with, the 

 lingual and palatal teeth in fishes, are present 

 in the Echidna. 



The female Narwhal seems to be eden- 

 tulous, but has the germs of two tusks in the 

 substance of the upper jaw-bones; one of 

 these becomes developed into a large and 

 conspicuous weapon in the male Narwhal, 

 and, accordingly, suggested to Linnaeus the 

 name, for its genus, of Monodon, meaning 

 single tooth : but the tusk is never median, 

 like the truly single tooth on the palate of 

 the Myxine ; and occasionally both tu.sks are 

 developed in the Narwhal. In another Ceta- 

 cean, the great Bottle-nose, or Hypervodon, 

 the teeth are reduced in the adult to two in 

 number, whence the specific name H. bidens, 

 but they are confined to the lower jaw. The 

 sharp-nosed dolphin (Zij)hius) has also but 

 two teeth, one in each ramus of the lower 

 jaw ; and this is, perhaps, a sexual character. 

 The Delphinus grisens has five teeth on each 

 side of the lower jaw ; but they soon become 

 reduced to two. Amongst the marsupial ani- 

 mals, the genus Tarsipes is remarkable for the 

 paucity as well as minuteness of its teeth. 



The elephant has never more than one 

 entire molar, or parts of two, in use on each 

 side of the upper and lower jaws ; to which 

 are added two tusks, more or less developed, 

 in the upper jaw. 



Some Rodents, as the Australian Water- 

 rats (Hydromys], have two grinders on each 

 side of both jaws ; which, added to the four 

 cutting teeth in front, make twelve in all : 

 the common number of teeth in this order is 

 twenty ; but the hares and rabbits have twenty- 

 eight teeth. The sloth has eighteen teeth. 

 The number of teeth, thirty-two, which cha- 

 racterises man, the apes of the old world, 

 and the true ruminants, is the average one of 

 the class Mammalia ; but the typical number 

 is forty-four. 



The examples of excessive number of teeth 

 are presented, in the order Enda, by the 

 Priodont Armadillo, which has ninety-eight 

 teeth ; and, in the cetaceous order, by the 

 Cachalot, which has upwards of sixty teeth, 

 though most of them are confined to the 

 lower jaw ; by the common porpoise, which 

 has between eighty and ninety teeth ; by the 



* Odontography, pi. 87 a, ff/s. 1 G. 

 t Ib. pi. 76, Jigs'. 4. 6 ; art. CETACEA, Vol. I. p. 572, 

 ./?<?. 259 b. 



Gangetic dolphin, which has one hundred 

 and twenty teeth ; and by the true dolphins 

 (Delpkimis), which have from one hundred to 

 one hundred and ninety teeth, yielding the 

 maximum number in the class Mammalia. 



Form. Where the teeth are in excessive 

 number, as in the species above cited, they 

 are small, equal, or subequal, and of a simple 

 conical form ; pointed, and slightly recurved 

 in the common dolphin ; with a broad and 

 flattened base in the gangetic dolphin (/?') ; 

 with the crown compressed, and broadest in 

 the porpoise ; compressed but truncate, and 

 equal with the fang, in the Priodon. The 

 compressed triangular teeth become coarsely 

 notched or dentatecl, at the hinder part of 

 the series, in the great extinct cetaceous Zeu- 

 glodon. The simple dentition of the smaller 

 Armadillos, of the Orycterope, and of the 

 three-toed Sloth, presents a difference in the 

 size, but little variety in the shape of the 

 teeth, which are subcylindrical, with broad 

 triturating surfaces ; in the two-toed Sloth, 

 the two anterior teeth of the upper jaw aiv 

 longer and larger than the rest, and adapted 

 for piercing and tearing. 



In almost all the other Mammalia, particular 

 teeth have special forms for special uses : 

 thus, the front teeth, from being commonly 

 adapted to effect the first coarse division of 

 the food, have been called cutters or incisors ; 

 and the back teeth, which complete its com- 

 minution, grinders or molars ; large conical 

 teeth, situated behind the incisors, and adapted 

 by being nearer the insertion of the biting 

 muscles, to act with greater force, are called 

 holders, tearers, laniaries, or more commonly 

 canine teeth, from being well developed in the 

 dog and other Carnivora, although they are 

 given, likewise, to many vegetable feeders 

 for defence or combat: e.g. Musk-deer (fig. 

 580, VII.). Molar teeth, which are adapted for 

 mastication, have either tuberculate, or ridged, 

 or flat, summits ; and usually are either sur- 

 rounded by a fence of enamel, or are tra- 

 versed by enamel plates arranged in various 

 patterns. Certain molars in the Dugong, 

 the Mylodon, and the Zeuglodon, are so 

 deeply indented laterally by opposite longi- 

 tudinal grooves, as to appear, when abraded, 

 to be composed of two cylindrical teeth ce- 

 mented together, and the transverse section 

 of the crown is bilobed. The teeth of the 

 Glyptodon were fluted by two analogous 

 grooves on each side. The large molars of 

 the Capybara and Elephant have the crown 

 cleft into a numerous series of compressed 

 transverse plates, cemented together side by 

 side. 



The teeth of the Mammalia have usually 

 so much more definite and complex a form 

 than those of fishes and reptiles, that three 

 parts are recognised in them : viz. the " fang," 

 the "neck," and the "crown." The fang or 

 root (radix) is the inserted part ; the crown 

 (corona] the exposed part ; and the construc- 

 tion which divides these is called the neck 

 (cerviv). The term " fang " is properly given 

 only to the implanted part of a tooth of re- 



