Page 201 - Clinical Anatomy

ECA3 7/18/06 6:45 PM Page 186

186 The upper limb

These intrinsic muscles, arising from the palmar aspect of the hand and
inserting along the dorsal aspects of the fingers, have the unique action in
that they flex the m/p joints and extend the i/p joints.
The interossei, together with abductor digiti minimi, are responsible for
abduction (dorsal interossei) and adduction (ventral interossei) of the
fingers. A weak abduction movement accompanies the action of extensor
digitorum and the long flexors adduct the fingers in the movement of full
flexion. However, if these movements of extension and flexion are elimi-
nated by laying the hand flat on the table, abduction and adduction become
purely the actions of the intrinsic muscles. A card gripped between the
fingers in this position of the hand is kept there entirely by intrinsic muscle
action.
The 5th finger receives two further intrinsic muscles, opponens digiti
minimi and flexor digiti minimi, from the hypothenar eminence.
The eight muscles acting on the thumb may be divided into the long
(proceeding from the forearm), and the short or intrinsic muscles.
•◊◊Long
flexor pollicis longus—inserted into the distal phalanx
extensor pollicis longus—into the distal phalanx
extensor pollicis brevis—into the proximal phalanx
abductor pollicis longus—into the metacarpal
•◊◊Short
adductor pollicis }
flexor pollicis brevis into the base of the proximal phalanx
abductor pollicis brevis
opponens pollicis—along the metacarpal
The flexors and extensors of the wrist play an important synergic role
in movements of the hand. Notice how weak the grip becomes when the
wrist is fully flexed; it must be held firmly in the extended or neutral posi-
tion by balanced muscle action in order to allow the long flexors of the
fingers and thumb to work at their full stretch and, therefore, at their
maximum efficiency.

The arteries of the upper limb

The axillary artery

The axillary artery commences at the lateral border of the first rib, as a con-
tinuation of the subclavian, and ends at the lower border of the axilla (i.e.
the lower border of teres major) to become the brachial artery. It is divided
into three parts by pectoralis minor and, apart from its distal extremity, it
lies covered by pectoralis major.
Above pectoralis minor, the brachial plexus lies above and behind
the artery, but, distal to this, the cords of the plexus take up their posi-
tions around the artery according to their names, i.e. lateral, medial and
posterior.