In the ulnar section the anterior surface of this muscle is in contact with the fascia; in the radial it is covered by the supinator radii longus, the two radial extensors, and crossed by the radial artery and nerve. The posterior surface of this muscle is in contact with the anterior ligament of the elbow-joint, the bra chialis anticus, the median nerve, ulnar artery, the flexor communis digitorum sublimis and radius. This muscle, while presenting a smooth and tendinous face to the under surface of the supinator longus and radial extensors, conti nues fleshy on its under surface to the very point of its connexion with the radius, the muscle beneath, whose surface is in contact with its fleshy fibres, being clothed in a similar manner with tendon ; this admirable contri vance for preventing friction is by no means peculiar to this situation, though its utility is frequently overlooked.
The name of this muscle indicates its action as a pronator of the hand, and when that effect has been produced, if its contractile power be still further excited, it will flex the fore-arm upon the upper. In case of fracture of the radius, this power is excited injuriously in bringing the radius across the ulna, and thus obliterating the interosseal space, and if not corrected by the surgeon, causing unnatural union of the two bones.
2. Flexor carpi radiolis ( ill.radialis intcrnus, Winslow, Al binus, Lieutaud, Sabatier, Soemarn.; grand palmaire, or radial anterieur, Cloquet ;) arises from the internal condyle of the humerus in common with the last-mentioned muscle; at the point where these two muscles are con nected with the humerus there exists no na tural separation between them. About an inch and a half from their origin a separation is eflbeted by the dipping in of the fascia forming one of the muscular septa previously referred to. At the lower part of the upper third of the fore arm their separation is complete. The flexor carpi radialis first changes its muscular fibres for tendinous on its anterior flee, and a rounded tendon is the result at the upper part of the lower third of the arm. This tendon passes in front of the wrist-joint and through a groove in the Gs trapezium, is ultimately inserted into the base of the metacarpal bone supporting the forefinger.
This muscle has on its outer edge, in the superior third of the fore-arm, the pronator radii teres, in the two inferior thirds the supi nator radii longus; the palmaris longus to its inner edge, both at its origin and throughout its whole course in the fore-arm. Anterior to it there is simply the fascia, its posterior face is in contact with the superficial flexor of the fingers above and the long flexor of the thumb below. The tendon of this muscle projects distinctly through the skin at the lower part of the arm.
The flexor carpi radians, besides flexing the whole hand on the fore-arm, bends the second row of carpal bones upon the first. It will also act as an abductor of the hand, in consequence of its being fixed on the outer side of the hand in the pulley-like groove of the trapezium through which it passes. It slightly assists the
pronator muscles in their influence over the hand.
3. The palmaris longus, Soeinm., cpitrochlo palmairc, Chauss. The origin of this muscle, which is in common with the other flexors, is from the inner condyle, also from a tendinous intermuscular septum which separates it from the flexor carpi radialis on the outer side and the flexor communis digitorum on the inner. This muscle, the smallest of those situated in the forearm, becomes tendinous midway be tween the elbow and wrist joint. This tendon, which is narrow and slender, descends to the annular ligament, and is ultimately connected with the palmar fascia. This fascia has some times been considered as a mere expansion of the tendon of the palmaris longus, but as the muscle is occasionally wanting and the fascia never, we regard it rather as another instance of that useful connexion of muscles with fascim which we have already had occasion to admire. This muscle, except at its origin where it has the flexor carpi radialis to its inner side and the flexor to the outer, maintains a posi tion completely superficial to the other muscles, its posterior face lying upon the flexor communis sublimis.
This muscle flexes the hand, and makes tense the palmar fascia and annular ligament, and thus takes off from the palmar vessels and nerves and the tendons of the digital flexors the pressure to which they are exposed when the hand grasps a solid body firmly; as, for in stance, when the whole weight of the body is sustained, as in the case of the sailor climbing the rigging of a vessel, by the power of the flexors of the fingers and hand.
4. Flexor communis digitorum sublimis per forates. (Alesculas perforates, Socmm., cpi trochlo-phalanginien commun, Chauss.) This muscle also arises from the inner condyle in common with the other muscles, and from a strong tendinous septum separating it from the flexor carpi ulnaris. About the middle of the fore-arm this portion of the muscle is joined by muscular fibres which arise from the radius im mediately below the insertion of the supinator radii brevis, and on the inner side of the pro nator radii teres. Between these two origins of the flexor communis digitorum is placed the median nerve. The tendinous fibres, into which the muscle is gradually transformed, become first apparent on the anterior surface, and next being collected ultimately split into four cords, which passing behind the annular ligament of the wrist, enter the palm of the hand ; oppo site the first phalanx of the four fingers these cords, splitting into two portions and allowing the passage of the deep flexors, terminate by being inserted in the rough edge on the sides of the second phalanges. The tendons of this muscle as well as the deep flexor are bound down to the phalanges by smooth tendinous sheaths or them which are dense and firm be tween the articulations, but insensibly disap pearing opposite the joint, where their presence would interfere with the motion of the parts; they are lined by synovial membrane to prevent unnecessary friction.