Abstract
In order to gain more comparative information on the proprioceptors related to the human jaw movement the muscle spindle distribution was investigated in the masticatory muscles of the squirrel monkey from the phylogenetic viewpoint of man through the primates. The present histological investigation showed that the muscle spindles, 270 in number, were distributed within a restricted area of the masticatory muscles on one side. Of these, 160 muscle spindles were concentrated in the inner lowermost layer of the horizontal (78 spindles) and vertical (82 spindles) portions of the temporalis muscle. The medial pterygoid muscle contained 57 muscle spindles. The masseter muscle contained muscle spindles, 47 in number, 24 spindles in the superficial portion and 23 spindles in the profundus. The zygomatico-mandibular muscle contained 6 spindles. The lateral pterygoid muscle was devoid of spindles.
