FORE-A am.—a. Superficial layer cf muscles.— On the radial side we observe two, supinator radii longus and extensor carpi radialis Ion gior.
1. Supinator radii longus, (grand supina tear, Cloq., brachio-radialis, Soemm.,) arises by a broad, flat, fleshy origin from the rough ridge, on the outer side of the lower extremity of the os humeri, which gradually terminates in the outer condyle; it is connected at the apex of its origin with the deltoid : it arises likewise from the intermuscular ligaments of the upper arm ; passing over the elbow-joint, its surfaces, which in the upper arm face outwards and in wards, are converted into anterior and posterior in the fore-arm ; opposite the tubercle of the radius it becomes tendinous on its under sur face, and the fleshy fibres on its anterior face entirely disappear about the middle of the fore arm in a flat tendon, which, narrowing as it descends, is inserted into the external edge of the base of the radius.
This muscle at its origin has to the inner side of it the brachialis anticus muscle and the radial nerve and superior profunda artery ; to its outer side and posteriorly the triceps ex tensor cubiti ; a little lower down and just above the elbow joint it has the extensor carpi radialis longior to its outer side, which maintains a uniform relation to it in its whole course ; in passing over the elbow-joint the tendon of the biceps flexor cubiti separates it from the bra chialis anticus; below the tendon of the biceps muscle, we meet with, first, the pronator radii teres in apposition with its internal edge ; and, next, the flexor carpi radialis. In contact with its posterior face superiorly is the supinator radii brevis ; below this muscle the tendon of the pronator radii teres ; and still lower down the flexor longus pollicis.
The supinator radii longus, in addition to its action as a supinator of the hand, is a flexor of the fore-arm upon the arm.
2. Extensor carpi radialis longior, (radi alis externus longior, Soemm., homer(' sus-me tacarpien, Chauss., Dumas,) arises from the lower extremity of the ridge above referred to, and from the outer condyle. Advancing for
ward it passes over the front of the elbow joint, and soon becoming tendinous on its an terior surface descends on the anterior part of the fore-arm, partly overlapped by the tendon of the supinator radii longus—its tendon gra dually seeks the posterior part of the arm, and running through a broad shallow depression appropriated to it and the second radial exten sor, finishes its course by being inserted into the back part of the metacarpal bone supporting the index finger. This muscle, as its name implies, is an extensor of the hand, possessing also a slight power in effecting its abduction.
In the ulnar section of the anterior super ficial antibrachial region we find five mus cles.
1. Pronator radii teres arises tendinous, above the elbow-joint from the intermuscular ligament of the upper arm, from the front part of the internal condyle of the os humeri, from the process of fascia separating it from the flexor carpi radialis, and from the ulna close to the insertion of the brachialis anticus. This muscle, though tendinous at its origin, soon becomes fleshy, and from its rounded form, which causes a distinct projection beneath the skin at the front and upper part of the fore-arm, derives its name. Its fleshy fibres terminate in a tendon as it enters the radial section, which gradually be comes wider as it descends, and sliding behind the supinator radii longus and extensor carpi radialis and in front of the radius, is inserted into the outer and back part of that bone. The pronator radii teres has to its outer side, supe riorly, the tendon of thebiceps muscle; below the tubercle of the radius it has the internal edge of the supinator radii longus in apposition with it, and as it slides in a spiral direction round the radius, and behind this muscle, it has the supinator radii brevis superior and external to it ; to its inner side it has throughout its course the flexor carpi radialis.