Morphology of the middle ear in the rhesus monkey (Macaca mulatta)

The purpose of this study was to provide a description of the morphology of the middle ear and related structures in the rhesus monkey, Macaca mulatta. From these descriptions, it can be seen that except for relative size differences, the middle ear system of the rhesus monkey bears close resemblance to that of man. The basic architecture is the same, thereby providing an anatomic foundation for the observed similarities in function [Cantekin et al,, 1981]. The few differences between the two systems can be summarized as follow: (1) The angle of inclination of the medial wall on the parasagittal plane is more acute in the rhesus monkey than in man. (2) The shape of the tympanic membrane in the monkey is almost circular compared to the irregular oval shape in man. (3) Differences in the shape of the ossicles as well as differences of relative measurements and angles between the parts of the ossicles were observed. (4) A major difference involves the pneumatic system and most prominently, the absence of a definite mastoid process in the monkey. However, the mastoid portion of the temporal bone is still very cellular in the majority of the specimens and communicates with the middle ear cavity through a well-defined mastoid antrum. The well-developed and extremely cellular petrous bulla in the monkey is absent in man.