246 THE DENTAL SYSTEM OF THE PRIMATES [SECT. A 



ANTHROPOIDEA. Simiidae. Simia satyrus (Orang-utan). 



Dental formula : cf. Hylobates. (Figs. 172 and 173.) 



In correspondence with the greater absolute bulk of these animals the 

 teeth of the larger Simiidae are larger than any others hitherto considered. 

 As in most of the Anthropoidea, the sexual factor has an important influence 

 upon the dentition and particularly upon the dimensions of the canine teeth. 

 The transitory dentition is found in all the Primates so far as they are 

 known ; in the case of the higher members of this Order (cf. Figs. 145 and 147) 

 a very close agreement with the phenomena presented by the Hominidae 

 has been observed, and in the lai'ger Simiidae the transitory teeth coi'respond 

 in number to those found in the milk dentition of the Hominidae. The 

 differences hitherto noticed affect the sequence in which the replacement 

 of the transitory by the permanent teeth occurs. 



To return to the teeth of the Orang-utan, we note (cf. Fig. 172) a large 

 diastema or interval in front of the upper canine teeth : the two upper pre- 

 molar teeth resemble one another more closely than in some forms previously 

 dealt with (e.g. Cercopithecidae). Both are bicuspid and furnished with three 

 roots ; in both the antero-posterior diameter of the crown is diminished : in 

 the first of the two, the outer or labial cusp surpasses in size the lingual 

 cusp. Like the remaining post-canine teeth, the crowns of the premolar teeth 

 are marked with fine crenations. 



The crowns of the three molar teeth exhibit crenate markings in a degree 

 which is peculiar to the Orang-utan among the Simiidae and in which it 

 is most nearly approached by the Chimpanzee. This crenation is the ex- 

 pression of folding of the enamel covering the crown and is a feature of 

 practically all developing molars in the Primates. Its persistence thus 

 constitutes the retention of an embryonic condition. When strongly marked, 

 and individuals present much variation in this respect, the features of the 

 dental crown are hereby obscured. Nevertheless it is possible to make out 

 some other points in the conformation of these teeth. The crowns are nearly 

 equilateral and traces of four cusps are commonly seen. The first and third 

 molar teeth are nearly equal in size and both are smaller than the second : 

 the last tooth seldom fails to bear signs of degeneration. Of the cusps, the 

 antero-internal and postero-external are joined by an oblique ridge similar to 

 that seen in Hylobates. The postero-internal cusp shews signs of degeneration 

 and reduction (it may be replaced by several minute eminences) before these 

 are exhibited by the other cusps. 



The lower canine tooth is long and tusk-like. The first premolar tooth is 

 pyramidal, and the labial cusp far surpasses the lingual cusp in size. The 

 two cusps of the second premolar tooth are subequal in size, and a suggestion 

 of a posterior projection, or talon, is seen (as in Hylobates). Crenation is 

 present as in the upper post-canine series. 



The molar teeth are longer than they are wide, the last tooth being the 

 smallest. The cusps are five in number, and the posterior intermediate cusp 

 is often found to be much reduced in prominence in the last tooth. 



