THE PALMAR FASCIA 333 



THE PALMAR FASCIA 



The palmar fascia takes the place of the deep fascia in the palm of the hand, 

 and is for tlie most part formed l^y the expansion of the tendon of the palmaris 

 longus. It is also continuous ■with the lower margin of the anterior annular liga- 

 ment. It may be divided into a central and two lateral portions. The central 

 division, which is by far the strongest, is of a triangular shape, the apex being con- 

 tinuous with the tendon of the palmaris longus, and also attached to the lower 

 border of the anterior annular ligament; the base corresponding to the heads of the 

 four inner metacarpal bones. It consists in front of longitudinally arranged bundles 

 of fibrous tissue derived from the palmaris longus tendon, and behind of transverse 

 fibres which continue those of the annular ligament. Below, the fascia divides into 

 four ])rocesses which join the ligamenta vaginalia of the finger tendons. Each of 

 these four jDrocesses forms a bridge across the tendons, and is inserted, at the sides 

 of the metacarpo-phalangeal joint, into the lateral and the deep transverse liga- 

 ments. This strong central portion of the palmar fascia is closely connected upon 

 its anterior surface with the skin by fibrous septa, which form small compartments 

 in wliich are lodged pellets of the subcutaneous fat. Upon its posterior surface it 

 is smooth and in contact Avith the synovial membrane of the great laalmar bursa 

 aljove. and of the thecse below. Between its four processes there are three spaces 

 left tln-ough which the digital nerves and arteries emerge. These are bridged over 

 l)y transverse fibres which connect the processes, and which form the superficial 

 transver-se lifjaments lying in the weljs between the fingers. 



The outer division, or thenar fascia, is that portion of the palmar fascia which 

 covers the ball of the thumb. It is connected above with the anterior annular 

 ligament, the tendon of the palmaris longus, and an aponeurosis from the tendon 

 of the extensor ossis metacarpi pollicis. After covering the short muscles of the 

 thumb, it is continuous below with the ligamentum vaginale of the flexor longus 

 pollicis tendon. The inner division, or hypothenar fascia, is of a triangular 

 shape, the base being above and the apex below. Arising from the anterior annular 

 ligament and the deep fascia of the forearm at the inner side of the wrist, it invests 

 the short palmar muscles peculiar to the little finger, and terminates upon the ulnar 

 border of the hand close to the fifth metacarpo-phalangeal joint. It is covered 

 above by the palmaris brevis. 



A deep layer of fascia covers the front of the interossei muscles, and is attached 

 by thin longitudinal septa to the posterior surface of the central part of the palmar 

 fascia. 



The ligamenta vaginalia are strong bands of transverse fibres which are 

 attached to the 1)orders of the first and second phalanges, and serve to bind in their 

 ])laces the long flexor tendons. Opposite the joints the ligaments are thin, and 

 composed chiefly of obliijuely decussating fibres. 



The sheaths of the flexor tendons, or thecae as they are called, are blind 

 tubes of synovial membrane which invest the back of the ligamenta vaginalia and 

 the front of the three phalanges and the interphalangeal joints. They extend from 

 the metacarpo-phalangeal joint to the middle of the last phalanx; and at the 

 extremities of the tube, the synovial membrane is reflected upon the surface of the 

 flexor tendons. Small folds and cords containing connective tissue and blood-vessels, 

 and invested by the synovial membrane, .^tretch across the intervening space. 

 These are called vincula accessoria (fig. 279 ). One set of these, the ligamenta 

 brevia, are of triangular shape, and pass directly forwards from the front of the 

 lower })art of the first and second phalanges to the back of the overlying tendons; 

 while the other set — which are called the ligamenta longa — are small cords run- 

 ning downwards and somewhat forwards from the plialanges to the tendons, at a 

 higher level than the ligamenta brevia. The compartment of the palmar Ijursa 

 belonging to the flexor longus pollicis tendon is continuous with the theca of 

 the tliumb. The theca also of the little finger is close to, and frequently in 

 communication with, the lower part of the great palmar bursa upon its ulnar side 

 (fig. 274). 



