On the "median buccal accessory cusp" in the upper molars of Macaca

Abstract

An accessory cusp occasionally appears between mesial buccal (Paraconus) and distal buccal cusps (Metaconus) of the upper molars of Macaca. BATUJEFF had already given attention to such kind of cusp (1893) and DE TERRA had reported this accessory cusp under the name of interstitieller Grubchenhocker without detailed description (1905).The author would like to name this accessory cusp asthe median buccal accessory cusp (Bucciconulus intermedius) to indicate its location and to discriminate it from Parastyle etc derived from the buccal cingulum of the upper molar.Configurations of the median buccal accessory cusp were investigated on 157 first molars, 152 second molars and 105 third molars out of 304 upper molar rows of Macaca irus. Additional examinations were made on the upper molars of Macaca mulatta, Macaca radiata, Macaca maura and Macaca cyclopsis for reference. All the inspections were carried out with a magnifying-glass (25 X).The results obtained are as follows:The median buccal accessory cusp is considered to be an accessory cusp found on the upper molars of Macaca in general.As far as the upper molars of Macaca irus are concerned, 19 first (12.1%), 22second (14.5%) and 22 third molars (21.0%) had cusps of this kind.Out of upper molars of Macaca irus having the above mentioned accessory cusp, 9 first, 13 second and 13 third molars had the accessory cusps located exclusively on the occlusal surface (Occlusal type), while 10 first, 9 second and 9 third molars had such an accessory cusp located on both occlusal and buccal surfaces spreading along the buccal groove (Occlusal-buccal type). The groove separating the accessory cusp from the distal buccal cusp is deeper and more distinct than that between the accessory cusp and the mesial buccal cusp. Accordingly the former must be the buccal groove itself. This might explain that the accessory cusp is located mesial to the original buccal groove, and is a part of the menial cusp of the upper molar.