This nerve accompanies the brachial artery, (Fig. VI, 11.) and therefore presents a similar surface marking. It is necessary, however, to bear in mind that the nerve crosses the artery superficially from above downwards and from without inwards. The median nerve in the forearm passes vertically downwards from the inner bicipital sulcus to the front of the wrist, (Fig. VI, 19.) there lying to the ulnar side of the flexor carpi radialis and under cover of the palmaris longus tendon. The nerve then passes under the anterior annular ligament to the palm.
The ulnar nerve in the upper third of the arm lies along the inner side of the brachial artery. It then leaves that vessel, (Fig. VI, 13.) and, accompanied by the inferior profunda artery, passes downwards and backwards to reach the hollow between the internal condyle and the olecranon process.
The ulnar nerve in the forearm corresponds in direction to a line drawn from the internal condyle of the humerus to the radial side of the pisiform bone. (Fig. VI, 20.) In front of the wrist the nerve lies to the radial side of the tendon of the flexor carpi ulnaris muscle, and subsequently passes superficial to the anterior annular ligament to its palmar distribution.
The palmar fascia is triangular in shape, the apex being attached to the anterior annular ligament between the thenar and hypothenar eminences, whilst the base corresponds to the proximal ends of the four inner fingers.
The upper transverse crease on the palmar aspect of the hand lies just below the normal limit of the superficial palmar arch, but at the level of the lower limit of the main flexor synovial sheath. The lower crease crosses the necks of the metacarpal bones, and corresponds to the upper limit of the distal flexor synovial sheaths.
The metacarpo-phalangeal joints lie about half-way between the distal crease of the palm and the proximal crease of the fingers. The middle and distal creases on the palmar aspect of the fingers correspond fairly accurately to the respective interphalangeal joints. The " knuckles" are formed by the heads of metacarpal bones.