490 



THE MUSCLES AND FASCIA. 



the diverticulum is continued on, and communicates with the synovial sheath of the 

 tendons. In the other three fingers the synovial sheath of the tendons in the fingers 

 begins as a blind pouch without communication with the large synovial sac (Fig. 313). 



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

 abscess in the thuinb and little finger is liable to be followed by abscesses in the forearm, from exten- 

 sion of the inflammation 



ANNULAR LIGAMENT. 



FLEXOR LONGUS pOLLicis. I Median nerve. 



FLEXOR CARPI RADIAL1S. \ I / JJlndT VCSS 



MUSCLES OF THUMB, \ \ III /PALMARIS BREV1S. 



1st Metacarpal. 



EXT. PRIM 



INTERNOD. 



POLL. 



EXT. SEC 

 INTERNOD. 



POLL. 



Trapezium! 



Radial vessels. 



EXT. CARP. RAD. LONG. 



Trapezoid. 



EXTENSOR CARPI RADIALIS 

 BREVIOR. 



MUSCLES OF 

 LITTLE 

 FINGER. 



EXT. CPRPI 

 ULNARIS. 



EXTENSOR 

 MINIMI 

 DIGIT). 



EXTENSOR 



COMMUNIS 



DIGITORUM. 



along the continuous 

 synovial sheaths. Gan- 

 glion is apt to occur in 

 this situation, constitu- 

 ting "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 correspond- 

 ing to the annular liga- 

 ment between the two. 

 The fluid can be forced 

 from the one swelling to 

 the other under the liga- 

 ment. 



EXTENSOR INDICIS. 



Os magnum. The Posterior An- 



PIG. 312. Transverse section through the carpus, showing the relative posi- nular Ligament IS a 

 tions of the tendons, vessels, and nerves. (Henle.) strong; fibrous band 



extending transversely 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 forms a sheath for 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 digiti ; 



FIG. 313. 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. 314) 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 



