MUSCLES OF THE UPPER EXTREMITY  .—The deltoid (see

figs.7and8) is the muscle which forms the shoulder cap and is used in abducting the arm to a right angle with the trunk; it runs from the clavicle, acromial process and spine of the scapula, to the middle of the humerus, and is supplied by the circumflex nerve, Several shortthe biceps (fig . 7), the long head of which rises from the top of the glenoid cavity inside the joint, while the short head comes from the coracoid process . The insertion is into the tubercle of the radius . These three muscles are all supplied by the same (musculo-cutaneous) nerve . At the back of the arm is the triceps (fig . 8) which passes behind both shoulder and elbow joints and is the great extensor muscle of them; its long head rises from just below the glenoid cavity of the scapula, while the inner and outer heads come from the back of the humerus . It is inserted into the olecranon process of the ulna and is supplied by the musculo-spinal nerve . The muscles of the front of the forearm form superficial and deep sets (see fig . 7) . Most of the superficial muscles come from the internal condyle of the humerus . From without inward they are the pronator radii teres going to the radius, the flexor carpi radialis to the base of the index metacarpal bone, the palmaris longus to the palmar fascia, the flexor sublimis digitorum to the middle phalanges of the fingers, and the flexor carpi ulnaris to the pisiform bone . The important 56 points of practical interest about these muscles are noticed in the article ANATOMY (Superficial and Artistic) .

In addition to these the brachio-radialis is a flexor of the forearm, though it arises from the outer supracondylar

ridge of the humerus . It is supplied by the musculo-spiral nerve, the flexor carpi ulnaris by the ulnar, the rest by the median . The deep muscles of the front of the forearm consist of the flexor longus pollicis running from the radius to the terminal phalanx of the thumb, the flexor profundus digitorum from the ulna to the terminal phalanges of the fingers, and the pronator quadratus phalanges of the fingers, the extensor minimi digiti, the extensor carp ulnaris passing to the metatarsal bone of the minimus, and the supinator brevis wrapping round the neck of the radius to which it is inserted . The aconeus which runs from the external condyle to the olecranon process is really a part of the triceps .