PROBLEMS OF HUMAN DENTITION 105 



be admitted, for in this Anthropoid the third mohir is ahvays 

 a strongly developed element. But a fourth molar, of a rudi- 

 mentary shape and size, occurs also in man. And with regard 

 to the posterior end of the human denture, nearly all morpholo- 

 gists agree in the opinion, that this end is in a state of retrogression. 

 The third molar, esjiecially in the upper jaw of the white race, 

 is usually of a reduced size and often fails entirely. Selenka him- 

 self asserts, that in man this molar is characterized by a ten- 

 dency to retrogression. De Terra's researches indicate that in the 

 dentition of Europeans this tooth fails in fully 12 per cent. There- 

 fore the hypothesis of Selenka is contradictory. In the Orang 

 the distal end of the denture bears a progressive character, 

 because it produces a fourth molar; in man the same end l)ears 

 a regressi\'e character, and notwithstanding this fact, it also can 

 l^roduce a fourth molar. I therefore infer that the hy]:)othesis 

 of Se'enka brings no solution of the problem and that it pre- 

 sents even more difficulties owing to the theory that the fourth 

 molar in man and apes is an atavistic element. 



But as jiointed out already, the occurrence of a fourth molar 

 in man, does not warrant a direct phylogenetic interpretation. 

 Even such morphologists as Wilson and Charnock Bradley hesi- 

 tate to advance such a theory, and adopt Bateson's view that the 

 appearance of a fourth molar cannot w'ell be explained by refer- 

 ence to ancestral forms, since the four-molar type must be 

 regarded as too remote. Therefore these authors believe the 

 supernumerary molar is a variation merely resulting from a 

 dental germ in excess of the normal number, protiuced l)y the 

 unusual distally prolongated dental lamina. They therefore 

 agree, in a fundamental point, with the opinion maintained by 

 Zuckerkandl. It is clear that the main cause for the denial of 

 the atavistical significance of the fourth molar, is the fact that we 

 must go back until we reach the common ancestors of manmials, 

 to encounter beings with an increased normal number of molars. 

 And tliis is an objection of great value, if a true one. But this 

 is not the case. To understand the fourth molar of man and 

 ai)es as a reversion we need to trace the line of evolution no farther 

 back than to ancestoi-s with a platyrrhine structure of dentition. 



