402 



THE MUSCLES AND FASCIAE. 



tendons begins as a blind pouch without communication with the large synovial 

 sac (Fig. 240). 



Surgical Anatomy. This arrangement of the synovial sheaths explains the fact that 

 thecal abscess in the thumb and little finger is liable to be followed by abscesses in the forearm, 

 from extension of the inflammation along the continuous synovial sheaths. Ganglion is apt to 

 occur in this situation, constituting ''compound palmar ganglion" ; it presents an hour-glass 

 outline, with a swelling in front of the wrist and in the palm of the hand, and a constriction 

 corresponding to the annular ligament between the two. The fluid can be forced from the one 

 swelling to the other under the ligament. 



The Posterior Annular Ligament is a strong fibrous band extending obliquely 

 downward and inward across the back of the wrist, and consisting of the deep 

 fascia of the back of the forearm, strengthened by the addition of some transverse 

 fibres. It binds down the extensor tendons in their passage to the fingers, 



being attached, internally, to the styloid 

 process of the ulna, the cuneiform and 

 pisiform bones ; externally, to the margin 

 of the radius ; and, in its passage across 

 the wrist, to the elevated ridges on the 

 posterior surface of the radius. It pre- 

 sents six compartments for the passage 

 of tendons, each of which is lined by a 

 separate synovial membrane. These are, 

 from without inward 1. On the outer 

 side of the styloid process, for the ten- 

 dons of the Extensor ossis metacarpi 

 and Extensor brevis pollicis ; 2. Behind 

 the styloid process, for the tendons of 

 the Extensor carpi radialis longior and 

 brevior; 3. About the middle of the 

 posterior surface of the radius, for the 

 tendon of the Extensor longus pollicis ; 

 4. To the inner side of the latter, for the 

 tendons of the Extensor communis digi- 

 torum and Extensor indicis ; 5. Oppo- 

 site the interval between the radius and 

 ulna, for the Extensor minimi digit! ; 



FIG. 240. Diagram showing the arrangement of the 6. Grooving the back of the ulna, for the 



tendon of the Extensor carpi ulnaris. 



The synovial membranes lining these sheaths are usually very extensive, reach- 

 ing from above the annular ligament, down upon the tendons for a variable 

 distance on the back of the hand. 



The deep palmar fascia (Fig. 241) forms a common sheath which invests the 

 muscles of the hand. It consists of a central and two lateral portions. 



The central portion occupies the middle of the palm, is triangular in shape, of 

 great strength and thickness, and binds down the tendons and protects the ves- 

 sels and nerves in this situation. It is narrow above, where it is attached to the 

 lower margin of the annular ligament, and receives the expanded tendon of 

 the Palmaris longus muscle. Below, it is broad and expanded, and divides 

 into four slips for the four fingers. Each slip gives off superficial fibres, 

 which are inserted into the skin of the palm and finger, those to the 

 palm joining the skin at the furrow corresponding to the metacarpo-phalangeal ar- 

 ticulation, and those to the fingers passing into the skin at the transverse fold at 

 the base of the fingers. The deeper part of each slip subdivides into two proc- 

 esses, which are inserted into the lateral margins of the anterior (glenoid) liga- 

 ment of the metacarpo-phalangeal joint. From the sides of these processes 

 offsets are sent backward, to be attached to the borders of the lateral surfaces of 



