The short flexor muscle of the thumb, of which Bischoff has denied the existence, is certainly present in these animals. In the chimpanzee the lower fibres of the short abductor muscle of the thumb have their origin in the sesamoid bone. The middle fibres, of the same muscle issue from the strips of ligament attached to the sesamoid bone. On the other hand, the upper part of the muscle has its origin in the anterior annular ligament. In the orang, the lower fibres of the short abductor of the thumb likewise have their origin in the sesamoid bone, while the central fibres again start from the anterior annular ligament. The upper fibres are strong, and are inserted into the base of the first metacarpal bone. In a dissection of the orang the flexor longus pollicis sent a thin, tendinous expansion on to the bone. This sesamoid bone is also found in the gorilla, although Duvernoy and Rosenberg do not appear to be aware of its existence.[72] In the palm of the gorilla’s hand there is a short abductor, a short bicipital flexor, an opponens, and an abductor of the thumb. The longer belly of the short flexor extending in a more radial direction, and in connection with the opponens, is only slightly developed. In the muscular system of a gorilla’s little finger we may observe an abductor, a short flexor, and an opponens. The palm of the chimpanzee displays a short abductor, an opponens, a short bicipital flexor, and an adductor of the thumb; also an abductor, a short flexor, and an opponens of the little finger. In the orang I observed a short abductor, a short flexor with two bellies, an opponens, and an adductor of the thumb. In addition to the short flexor of the thumb, Langer and Bischoff describe another short, independent muscle, representing the long flexor, and attached to the second phalanx, but I have not myself ascertained the existence of this muscle. The same anatomists mention an adductor between the third metacarpal bone and the first joint of the thumb, and another between the second metacarpal bone and the second joint of the thumb, passing on into the extensor tendon. I am myself convinced of the existence of a twofold adductor, but not of the fact that the tendon of one of the muscles (termed by Langer the second opponens) passes on into the extensor tendon. In the little finger of the orang there is an abductor, a short flexor, and an opponens. In the gibbon there is a short abductor, a faintly indicated opponens, a short bicipital flexor, and an adductor of the thumb. In _Hylobates albimanus_ this adductor divides into four or five portions, which are attached to the whole of the first metacarpal bone. In the little finger there is an abductor, a short flexor, and an opponens. In the same animal the first inter-osseous muscle is attached by one portion to the second metacarpal bone, by the other to the base of the second phalanx of the index finger (Fig. 53, ~9~, ~10~).