The forearm has the shape of a somewhat flattened cone, being large above and small below. This is because the bellies of the muscles lie above and their tendons below. Most of the muscles of the forearm go to the hand and fingers. The prehensile functions of the hand require a strong grasp; hence it is that we find the flexor muscles on the anterior surface of the forearm much larger and more powerful than the extensors posteriorly, and the bones of the forearm, the radius and ulna, nearer the surface posteriorly.

Anterior Surface

Anteriorly nothing is to be felt except muscles and tendons. The extent to which these can be outlined depends on the absence of subcutaneous fat and the degree of development and contraction of the individual muscles. The skin of the forearm is loose and thin. Through it can be seen anteriorly, the median vein going up the middle and the radial vein winding around the back of the wrist and crossing the outer edge of the radius about its middle. On the inner side near the elbow the anterior and posterior ulnar veins are visible passing posteriorly.

Fig. 327. - Surface anatomy of the forearm.

Sometimes there is a slight depression on the inner side below the medial (internal) condyle which is caused by the bicipital fascia holding the muscle down. The biceps tendon can be felt at the bend of the elbow, and immediately below it for the distance of 5 cm. (2 in.) can be felt a hollow, the antecubital fossa. The mass of muscles between it and the ulna on the inside and posteriorly are the flexors and pronator radii teres; the mass of muscles on the outer side between it and the radius posteriorly are the extensors, supinator (brevis), and brachioradialis. The inner edge of the brachioradialis is indicated by a line drawn from the outer side of the biceps tendon to the outer surface of the styloid process of the radius. A line from the medial (internal) condyle running obliquely across the forearm to the middle of the radius indicates the pronator radii teres muscle. A line from the medial condyle to the middle of the wrist indicates the palmaris longus muscle; it is sometimes absent. Another line from the same point above to a centimetre to the radial side of the palmaris longus tendon at the wrist indicates the flexor carpi radialis muscle. The tendons of both these muscles can readily be seen. A line drawn from the medial (internal) condyle to the pisiform bone at the wrist indicates the anterior edge of the flexor carpi ulnaris muscle.

Fig. 328. - Surface anatomy of the back of the forearm.

Having located the superficial muscles the arteries and nerves can be traced. The brachial artery bifurcates about a finger's breadth below the bend of the elbow. A line drawn from the inner edge of the biceps tendon, or a point midway between the two condyles, to the anterior surface of the styloid process of the radius indicates the course of the radial artery. In the upper half of the forearm it is overlapped by the edge of the brachioradialis. In the lower half it is uncovered by muscle and lies in the groove formed by the brachioradialis on the outer side and the flexor carpi radialis on the inner. The ulnar artery describes a marked curve toward the ulnar side until it reaches the middle of the forearm, when it passes down in a straight line from the medial (internal) condyle to the radial side of the pisiform bone.

The median nerve runs down the middle of the forearm, lying beneath the groove separating the palmaris longus and flexor carpi radialis tendons. The ulnar nerve runs from the groove between the medial (internal) condyle and olecranon process above to the radial or outer side of the pisiform bone below. It lies to the ulnar side of the ulnar artery in the lower half of the forearm. The rounded muscular mass between the edge of the flexor carpi ulnaris and the palmaris longus is formed by the flexor sublimis digitorum muscle (Fig. 327).