The Comparative Anatomical Study of the Masseter of the Mammal (II)

Abstract

In all mammals described in this report, the masseter consists of the proper masseter group which includes the first superficial, second superficial, intermediate and deep masseters and the improper masseter group which consists of the maxillo- and zygomaticomandibular muscles. These muscular elements can be identified exactly in every animal investigated. The special features are described as follows: 1) In the red kangaloo, the first superficial, second superficial and intermediate masseters are thin, though broad. The deep masseter group makes especially a good development, namely, the pars anterior is identified in the first and second layers and the pars posterior can be divided into the first-fifth layers. The improper masseter group which includes the maxillo- and zygomaticomandibular muscles makes a good development, which is comparable to those of the carnivorous animal. 2) In the primate, the transitional change of the zygomaticomandibularis from the zygomatic arch to the supraorbital torus is pursued from the lower to the higher forms. In the galago, the muscle takes its origin from the zygomatic arch. In the squirrelmonkey, it originates not only from the zygomatic arch, but also spreads over the superficial temporalis, making the semicircular plate. In the chimpanzee, the muscle spreads between the superficial and deep temporales, connecting the lateral portion of the supraorbital torus with the coronoid process as in the human masseter. © 1965, Editorial Board of Okajimas Folia Anatomica Japonica. All rights reserved.