922 



TEETH. 



from the Old World Quadrumana more than 

 the Cebidcs do ; i. e. they differ not only in having 



four teeth (p. 2 r^r)* which the monkeys of 

 the Old World do not possess, but also by 

 wanting four teeth (m. 3 j3T[)' wnich those 



monkeys, as well as the Cebidce, actually have. 

 It is thus that the investigation of the exact 

 honiologies of parts leads to a recognition of 

 the true characters indicative of zoological 



affinity, 



33 

 Most of the Lemurintc have p. ^ ^ . 



f , together with remarkable modifications 



of their incisive and canine teeth, of which 

 an extreme example is shown in the pectinated 

 tooth (Jig. 556.) of the Galeopithecus. The 

 inferior incisors slope forwards in all, and 

 the canines also, which are contiguous to 

 them, and very similar in shape. In the 

 Chirogalcus these canines are entered as in- 

 cisors in the dental formula of the genus 

 (Vol. IV. p. 215), and the laniariform prernolar 

 (p. 2) is entered as a canine : M. Vrolik also 

 describes four teeth on each side of the upper 

 jaw, and four on each side of the lower jaw, 

 as true tuberculated molars. They have tuber- 

 culated crowns, but the value of shape as a 

 character is too small to permit our accepting 

 so great an anomaly without the requisite 

 proof of their order of development and suc- 

 cession. 



Even in the hoofed quadrupeds with toes 

 in uneven number (Perissodactyla)> whose 

 premolars, for the most part, repeat both the 

 form and the complex structure of the true 

 molars, such premolars are distinguished by 

 the same character of development as those 

 of the Artiodacty/a, or Ungulates with toes in 

 even number ; although in these the premolars 

 are distinguished also by modifications of size 

 and shape. The complex ridged and tuber- 

 culate crowns of the second, third, and fourth 

 grinders of the Rhinoceros, Hyrax (fig. 590.), 



tooth be determined, and its proper symbol 

 applied to it. 



In pi. 136, Jig. 5, of my Odontography, the 

 three posterior teeth of the almost uniform 

 grinding series of the horse's dentition are 

 thus proved to be the only ones entitled to 

 the name of " true molars ;" and, if any one 

 should doubt the certainty of the rule of count- 

 ing, by which the symbols, p. 4, p. 3, and p. 2, 

 are applied to the three large anterior grinding 

 teeth (ib.Jig. 19), which are commonly the 

 only premolars present in each lateral series of 

 the horse's jaws, yet the occasional retention 

 of the diminutive tooth, p. 1 (ib.JZg. 6), would 

 establish its accuracy, whether such tooth be 

 regarded as the first of the deciduous series 

 unusually long retained, or the unusually small 

 and speedily lost successor (p. 1) of an abortive 

 d 1. 



The law of development, so beautiful for 

 its instructiveness and constancy in the pla- 

 cental Diphyodunts, is here illustrated in the 

 little Hyrax (Jig. 591.), in which the d. 1 is 



Fix. 591. 



Deciduous and permanent molars of the Hyrax. 



normally developed and succeeded by a per- 

 manent p. 1, differing from the rest onty by a 

 graduated inferiority of size, which, in regard 

 to the last premolar, ceases to be a distinction 

 between it and the first true molar. 



The elephant, which by its digital characters 

 belongs to the odd-toed, or perissodactyle, 

 group of Pachyderms, also resembles them in 

 the close agreement in form and structure of 

 the grinding teeth representing the premolars, 



Fig. 590. 



Molar series, upper jaw (Ilyi'ax). 



and horse, no more prove them to be true with those that answer to the true molars of 

 molars, than the trenchant shape of the lower the Hyrax, Tapir, and Rhinoceros. The gi- 

 carnassials of the lion proves them to be false gantic Proboscidian Pachyderms of Asia and 



molars. It is by development alone that the 

 primary division of the series of grinding teeth 

 can be established, and by that character 

 only can the homologies of each individual 



Africa present, however, so many peculiarities 

 of structure, as to have led to their being 

 located in a particular family in the Systematic 

 Mammalogies. And this seems to be justified 



