Fig. 52.--Palmar muscles of gorilla. _a_, Anterior ligament. _b_, Remains of the skin of palm, here covered with a very sinewy skin. _c_, _f_, Oblique fibres of the ligaments of the sheath of the flexor tendons of fingers. 1, 2, Flexor tendons. 3, Spaces between the heads of the flexor brevis pollicis, whence in man the tendon of the flexor longus pollicis issues (comp. Fig. 51, ~5~). 4, 3, 3′, 5, Abductor, flexor brevis, abductor pollicis. 6, 7, 8, Opponens, flexor brevis, abductor, minimi digiti. 9, Dumbricales. 10, Supinator longus. 12, Flexor sublimis digitorum. 13, Flexor minimi digiti. 14, Flexor carpi ulnaris. ] In the chimpanzee I observed a superficial flexor, common to the fingers, and enlarged in the region of the third and little fingers. A superficial flexor, belonging to the index finger, started from the inner condyle of the humerus, and from the back of the inter-muscular septum. The deep finger-flexor was attached to the four fingers. In the orang the first of these flexors forms a two-tendoned belly for the index finger, as well as one for the other three fingers. The deep flexor only displayed two bellies. In the gibbon, on the other hand, the superficial flexor displays four bellies. [Illustration: Fig. 53.--Muscular system of the back of a gibbon’s hand. 1, The extensor carpi radialis longior and brevior. 2, Abductor longus pollicis. 3, Extensor primi internodii pollicis. 4, Extensor secundi internodii pollicis. 5, Extensor communis digitorum. 6, Extensor indicis. 7, Extensor minimi digiti. 8, Extensor carpi ulnaris. 9, First dorsal inter-osseous muscle. 10, Continuation of the same to index finger. 11, 12, The other inter-osseous muscles of this region. A, The posterior annular ligament. ] In the carpus of the chimpanzee there is, so far at least as my experience goes, a so-called sesamoid bone. It is in this instance in connection with the scaphoid and trapezium bones, just where the fibres of the anterior and posterior ligaments of the wrist pass into each other. In the chimpanzee the tendon of the long abductor muscle of the thumb sends some fibres into this sesamoid bone, while the other fibres of the tendon of this muscle, which divides into several strips, are inserted in the trapezium bone, and a few also in the base of the first metacarpal bone.