The outer ear form is strongly governed by genes. How the ear form varys among isolated groups of the same species is of interest in population genetics. From comparative anatomical point of view, it seems effective to apply the outer ear form as one of the determining basis of species. But, until now, there is scarcely any description of the ear of ape or monkey.
Thirty-seven monkeys (Macaca irus) consisting of 8 Philippine-born, 9 Thailand-born, 13 Malaya-born and 7 unknown were observed. In addition, 2 Formosa-born and Rhesus monkey were examined.
As classification of the outer ear form, an ear is divided into four parts ; upper part, Darwinian tubercle, outer contour and ending part of the ear. Each individual characteristics which are shown in Figure 1 to 6 were selected and classified considering the form of portions and the grade of development.
The analysed data on the intraspecific variation among Philippine, Thailand and Malaya groups are as follows:
Philippine: L_h-1M_0-1D₁R
Thailand: L_h-n-1M_1-2A-D_0-1-2R
Malaya: L_h-2T-M_0-1D₁R