DEVELOPMENT OF THE TEETH IN MAMMALIA 35 



and monkeys the upper teeth were, almost without excep- 

 tion, triangular. In the late Eocene or early Miocene Age, 

 the spur or talon was developed, and the triangular became 

 a quadricuspidate tooth. 



In Plate II, fig. B, which is also adapted from Osborn, the 

 cusps of the trigon are coloured red, and those of the talon 

 blue. In Anaptomorphus (fig. B T ) , a lower Eocene form allied 

 to Tarsius, a lemurine animal, the trigon only is present, the 

 protocone being internal and the paracone and metacone, 

 forming the base of the triangle, external. 



In fig. B 2 , a molar of an upper Eocene monkey, in addition 

 to the trigon a cusp has appeared, the hypocone, from an 

 upgrowth of the cingulum, and forms the talon of the upper 

 molars. 



In fig. B 3 , the molar of an Eskimo, the hypocone is very 

 fully developed, as, owing to the nature of the food of these 

 people, the teeth are very little used in mastication. 



Fig. B 4 , from a negro, shows the cusps of the trigon and 

 talon as seen, in the normal human upper molar tooth. 



It is thus seen that the four upper molar cusps represent 

 the three cusps of the original tritubercular tooth (the 

 trigon) and one cusp of the added talon, the hypocone. 



Upper Molars. 



Anterior palatal Protocone ) _ . 

 . Primitive triangle or 



Anterior buccal Paracone Y T . 



Posterior buccal Metacone j 



Posterior palatal Hypocone Primitive heel or Talon. 



Lower Molars. Although in the early ancestors of man 

 the three elements of the trigon were represented (fig. 10), 

 in the lower molars of human teeth- the paraconid is 

 suppressed, and only the protoconid and metaconid of 

 the original triangle remain, the three other cusps of the 

 quinquecuspidate lower molar being formed by the talonid. 

 The suppression of the paraconid is considered to be due 

 to the antagonism of the upper and lower molars not allowing 

 of its persistence in man. In Miacis, a form from the lower 

 Eocene (Plate II, fig. CJ, the trigonid is seen in all the three 

 molars, and, according to Osborn, shows ' how the primitive 

 anterior portion (trigonid) of the crown was reduced to the 



D 2 



