290 DISSECTION OF THE UPPER LIMB. 



extensors of the wrist; and a very small space for the extensor of the 

 second phalanx of the thumb follows on the ulnar side. Farther to the 

 inner side is the common sheath for the extensor of the fingers, and that 

 of the fore finger ; and then comes a separate compartment for the exten- 

 sor of the little finger. Internal to all is the space for the extensor carpi 

 ulnaris. The last muscle grooves the ulna ; but the others lie in hollows 

 in the radius in the order mentioned above, with the exception of the ex- 

 tensor minimi digiti, which is situate between the bones. 



Dissection. If the supinator brevis be divided by a vertical incision, 

 and reflected from the radius, its attachment to the bone will be better 

 understood. 



The posterior interosseous nerve, and the offsets from its gangliform 

 enlargement, may be traced more completely after the tendons of the ex- 

 tensor of the fingers and indicator muscle have been cut at the wrist. 



The dorsal surface of the posterior interossei muscles of the han-1 may 

 be cleaned, so that their double origin, and their insertion into the side, 

 and on the dorsum of the phalanges, may be observed. Between the heads 

 of origin of these muscles the posterior perforating arteries appear. 



SECTION VII. 



LIGAMENTS OF THE SHOULDER, ELBOW, WRIST, AND HAND. 



Directions. The ligaments of the remaining articulations of the limb, 

 which are still moist, may be examined at once ; but if any of them have 

 become dry, they may be softened by immersion in water, or with a wet 

 cloth, whilst the student learns the others. 



Dissection. For the preparation of the external ligaments of the 

 shoulder-joint the tendons of the surrounding muscles, viz., subscapularis, 

 supra and infraspinatus, and teres minor, must be detached from the cap- 

 sule ; and as these are united with it, some care will be needed not to 

 open the joint. 



SHOULDER JOINT. This ball and socket joint (fig. 89) is formed be- 

 tween the head of the humerus and the glenoid fossa of the scapula. In- 

 closing the articular ends of the bones is a fibrous capsule lined byasyno- 

 vial membrane. A ligamentous band (glenoid ligament) deepens the 

 shallow scapular cavity for the reception of the large head of the humerus. 



The bones are but slightly bound together by ligamentous bands, for, 

 on the removal of the muscles, the head of the humerus may be drawn 

 from the scapula for the distance of an inch. 



The capsular ligament (fig. 7f>, 5 ) surrounds loosely the articular ends 

 of the bones ; it is thickened above and below, and receives fibres from 

 the contiguous tendons. 



At the upper edge it is fixed around the articular surface of the scapula, 

 where it is connected with the long head of the triceps. At the lower 

 edge the ligament is fixed (fig. 89) to the neck of the humerus close to 

 the articular surface above, but at a little distance therefrom below ; and 

 its continuity is interrupted between the tuberosities (6) by the tendon 

 of the biceps muscle, over which it is continued along the bicipital 

 groove (fig. 7o). On the inner side there is generally an aperture in the 



