Intrinsic Hand Muscles of the Japanese Monkey, <i>Macaca fuscata</i>

Abstract

Anatomy of the intrinsic hand muscles in the Japanese monkeys was studied with an improved method to dissect the muscles and nerves in water after removal of the skeletal framework. The thenar eminence contained four muscles, namely m. abductor pollicis brevis, m. opponens pollicis, m. flexor pollicis brevis, and m. adductor pollicis. The hypothenar eminence contained four muscles, namely m. palmaris brevis, m. abductor digiti minimi, m. flexor digiti minimi brevis, and m. opponens digiti minimi. Majority of the thenar muscles are fused more or less with each other, so that clear separation of these muscles was difficult. The lumbrical muscles arose from the palmar parts of four main tendons of the deep flexor muscle to the second, third, fourth, and fifth digits. The mm. contrahentes arose mainly from a medial tendinous septum attached on the palmar surface to the third metacarpus, and included three muscles destined to the second, fourth and fifth digits. The interossei were found on the radial side of the second, third, fourth and fifth finger as well as on the ulnar side of the second, third and fourth finger. The intrinsic hand muscles in the Japanese monkey received innervation either from the median or the ulnar nerve. Branching pattern of these nerves to the individual muscles was fundamentally similar to those in man except for the fact that the median and the ulnar nerve in the Japanese monkey do not communicate to make a loop in the thenar muscles. A separate branch from the median nerve to the deep head of m. flexor pollicis brevis (accessory recurrent nerve) was described for the first time in the macaque monkey.