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Show 554 MR. J. BESWICK-PERRIN ON THE [Julie 20, the first phalanx of the fifth digit. There is a small sesamoid bone developed in the tendon of origin of the latter muscle. The muscles of the pollex are three in number :- 1. Abductor poliicis, which takes its origin from the radial sesamoid bone and the os trapezium. It is inserted into the radial side of the base of the first phalanx and its sesamoid bone. 2. The opponens poliicis arises from the trapezium. It is inserted into the distal part of the pollex metacarpal, and into the sesamoid bone on the radial side of the metacarpophalangeal articulation. 3. Flexor brevis poliicis consists of two portions : one arises from the trapezium, and is inserted into the sesamoid bone and base of first phalanx; the other arises from the trapezoid and os magnum, and 1 is inserted into the ulnar side of the base of the pollex proximal phalanx without impinging on the sesamoid bone. The pronator quadratus occupies almost the entire length between the two bones of the forearm. The interossei of the fore foot. There are only two superficial palmar interossei. They arise together by a thin flat tendon from the os magnum. Directly after their origin they diverge from each other: the one on the radial side terminates at the base of the first phalanx of the second digit on its ulnar side; the other (or ulnar side one) goes to the radial side of the base of the first phalanx of the fifth digit: the first abducts the index digit from the pollex ; the second adducts the fifth digit in the direction of the pollex. In the words of human myologists, both adduct towards a line drawn down the centre of either the third or fourth digit. The deep interossei are six in number: the first arises from the pollex and index metacarpal bases and shafts, the second and third from the interval between the second and third metacarpals; the fourth and fifth between the third and fourth, and the sixth between the fourth and fifth metacarpals. They are inserted as follows :-Each of the second, third, and fourth digits receives one on each side. There are two sesamoid bones in connexion with each metacarpo-phalangeal articulation ; and these muscles are connected respectively with each of them, and thus prolonged to the sides and bases of the proximal phalanges. The first, third, and fifth adduct the second, third, and fourth digits towards the pollex ; the second, fourth, and sixth abduct them from the pollex. These muscles can scarcely be called interossei; they are situated in a great measure upon the metacarpals rather than between them. The superficial ones are altogether removed from contact with the metacarpals. A good name for the deep layer would be " bilateral flexors." A n y two of these muscles acting conjointly would produce direct flexion of the first phalanx on to the metacarpal. This is probably their true use in the living subject. The Extensors of the Fore Limb. The supinator longus, the extensor carpi radialis longior and brevior are exactly the same as in the human subject. In the |