The M. Masseter of the Formosan Monkey

Abstract

A study of the M. masseter was made bilaterally according to the technique of Yoshikawa et al. on a sample of 25 Macaca cyclopis.1) A classification into the M. masseter superficialis (lamina prima and secunda), intermedius (lamina prima and secunda), profundus (lamina prima and secunda) and profundissimus was possible on the basis of the site and condition of origin and insertion, course of muscle bundles, etc. These parts were all supplied by branches from the N. massetericus.
2) The M. masseter superficialis lamina prima in many cases was found to show a formation corresponding to the pars reflexa of Rodentia.
3) In rare cases, conditions presumed to be variations of the M. masseter profundus were found.
4) The muscle located between the M. masseter and M. temporalis, with origin from the inner surface of the arcus zygomaticus and insertion into the lateral surface of the ramus mandibularis, which I called the M. masseter profundissimus is the part corresponding to the so-called M. zygomaticomandibularis of Toldt or the M. maxillomandibularis in the classification of Yoshikawa et al. The portion regarded as the M. zygomaticomandibularis by Yoshikawa et al. is an entirely different muscle from the M. zygomaticomandibularis of Toldt even though the nomenclature is the same and is a part of the M. temporalis.
The nerve supply also indicated that these parts belong to the M. masseter, and there was no apparent need to separate these parts and give them independent names as being part of the improper masseter group.