Occlusal Surface Pattern on the Molar of the Macaque

Abstract

As far as the catarrhine molars are concerned, the patterns of connection of cusps are divided into 3 types as follows; Type I indicates the connection between mesio-buccal and distolingual cusps, while the condition showing connection between mesiolingual and distobuccal cusps belongs to Type III. If the above mentioned 4 cusps come into contact with each other at a point, this feature is called Type II.The results obtained using this classification with molars of 350 macaque skulls are as follows.On the upper molar row, Type I is observed with extraordinary frequency on the first molar, while this pattern is recognized less frequently on the posterior molars. On the other hand, Type II and III increase materially towards the posterior molars, particularly II pattern is found remarkably on the second molar.On the lower molar row, however, Type I is very often recognized on all different kinds of molar at high rate and there is no remarkable difference concerning the distribution of this pattern among all the molars. Moreover, Type II and III as a whole are rarely observed on the lower molars.The findings on the human molars are opposite to those on the molars of the macaque, as will be mentioned below: Type III or its modification is considered to be found always on the upper molars in case of man, because it is certain that a diagonal ridge of the human upper molar suggests the existence of connection between mesiolingual and distobuccal cusps. Since Type I, II and III in the macaque and X, + and Y pattern of the human lower molars correspond to each other, it is quite natural that Type III should frequently be found on the mesial teeth and Type II or I on the distal teeth of the human lower molar row.Type III of the human molar could be considered as a primitive type in the evolution of the dentition in primates, while Type I of the macaque should be regarded as a specialized form which has secondarily developed.