CHAP. Vl] THE DENTAL SYSTEM OF THE PRIMATES 269 



pyriformis nasi: in each case, however, the tooth is imperfectly 

 formed 1 . 



The occurrence of teeth, more or less perfectly formed, in 

 dermoid cysts and ovarian tumours, must be regarded as beyond 

 the scope of the present account. 



IV. Variation by reduction in the number of the teeth. 



This is rare, but not unknown in the Primates other than the 

 Hominidae. In these, the numerical reduction is met with so 

 frequently that a definite trend in evolution is suggested. It is 

 possible that a similar process is affecting the Ateles type (South 

 American monkeys) and even Hylobates. 



Thus Ateles is characterized by the large number of anomalies 

 to which its dentition is liable, and this includes a tendency to the 

 loss of the last molar tooth (either in the upper or lower jaw) 2 . 

 This stage seems to have been reached by the Hapalidae (Mar- 

 tnozets). The Hylobatidae are said by Selenka 3 to be on the wax- 

 to lose not only the last molars but also the second premolar teeth. 

 An unusual anomaly in the ( )rang-utan, viz. the absence of the 

 third lower molar tooth, is recorded by Hrdlicka 4 . Absence of an 

 incisor tooth is on record in the case of several of the lower 

 Primates, and in one instance in the skull of a Gorilla"'. But 

 evidence for a "reduced dentition" does not become striking until 

 the Hominidae are reached' 5 . 



In Man and especially in the white races, the teeth first t«> be 

 suppressed are the third molars, and there is a distinct tendency 

 to the disappearance of the lateral incisor teeth. These changes 

 have been attributed to the progressive reduction of the jaws, a 



1 A corresponding case was described by Goethe in the last century : cf. also The 

 Lancet, Oct. 14, 1905, p. 114(i. 



2 Bateson, quoted by Ue Terra, op. cit., p. 286. 

 ■ : Selenka, v. De Terra, op. cit., p. 286. 



1 Proc. United States National Museum, Vol. xxxi. p. 539. 



5 Regnault, quoted by De Terra, up. cit., p. "286. 



6 Reduction has proceeded to even greater length in the Aye-Aye (Daubentonia 

 or Cheiromys). This Lemuroid is so aberrant from its associates, that it would 

 not be profitable to discuss its dentition in detail here. The difference between the 

 deciduous and permanent dentitions of the Aye-Aye is striking and very instructive. 



