922 



TEETH. 



from the Old World Quadrumana more than 

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



four teeth (p. 2 7), which the monkeys of 

 the Old World do not possess, but also by 

 wanting four teeth (m. 3 ]^T[) which those 



monkeys, as well as the Cebidce, actually have. 

 It is thus that the investigation of the exact 

 homologies of parts leads to a recognition of 

 the true characters indicative of zoological 

 affinity. 



33 

 Most of the Lemurincc have p. ^ , m. 



33 



-. together with remarkable modifications 



_> 7 O 



of their incisive and canine teeth, of which 

 an extreme example is shown in the pectinated 

 tooth (fig. 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 

 Chirogaleus these canines arc entered as in- 

 cisors in the dental formula of the genus 

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

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

 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 (Perissodactyld}, 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 Artiodacti/la, 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 (fg. 590.), 



tooth be determined, and its proper symbol 

 applied to it. 



In pi. 136, _//g. 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. fig. 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.fig. 6), would 

 establish its accuracy, whether such tooth be 

 regarded as the first of the deciduous scries 

 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 Dip/iyodunts, is here illustrated in the 

 little Hj/ra.c (fg. 591.), in which the d. 1 is 



Fig. 591. 



Deciduous mid permanent molars of the Ilyrux. 



normally developed and succeeded by a per- 

 manent p. 1, differing from the rest only 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 jcai) (Ilyrnx). 



and horse, no more prove them to be true 

 molars, than the trenchant shape of the lower 

 carnassials of the lion proves them to be false 

 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 eacli individual 



with those that answer to the true molars of 

 the Hyrax, Tapir, and Rhinoceros. The gi- 

 gantic Proboscidian Pachyderms of Asia and 

 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 



