282 DISSECTION OF THE FOREARM. 



attachment to the first phalanx ; and assist in the extension of the two 

 last phalangeal joints through their union with the extensor tendon. 



Further they can separate and approximate the fingers : thus the palmar 

 set adduct to the second finger ; and the dorsal abduct from the middle 

 line of the second finger the two attached to this digit moving it to the 

 right and left of that line. 



Dissection. The attachments of the annular ligament to the carpal 

 bones on each side are to be next dissected out by taking away the small 

 muscles of the thumb and little finger. Before reading its description, 

 the ends of the cut ligament nr<iy be placed in apposition. 



The anterior annular ligament is a firm ligamentous band, which arches 

 over and binds down the flexor tendons of the fingers. It is attached ex- 

 ternally to the front of the os scaphoides, and to the fore and inner parts, 

 and ridge of the os trapezium ; and internally to the unciform and pisiform 

 bones. By its upper border it is connected with the aponeurosis of the 

 forearm ; and by its anterior surface it joins the palmar fascia. On it lie 

 the palmaris longus and the ulnar artery and nerve. 



Dissection. Next follow the tendon of the flexor carpi radialis through 

 the os trapezium to its insertion into the metacarpal bones. 



The tendon of the flexor carpi radialis, in passing from the forearm to 

 the hand, lies in the groove in the os trapezium between the attachments 

 of the annular ligament to the bone, but outside the arch of that ligament ; 

 here it is bound down by a fibrous sheath lined by a synovial membrane. 

 The tendon is inserted into the base of the metacarpal bone of the index 

 finger, and sends a slip to that of the middle digit. 



SECTION VI. 



THE BACK OF THE FOREARM. 



Position. During the dissection of the back of the forearm the limb lies 

 with the forepart undermost, and a small block is to be placed beneath the 

 wrist for the purpose of stretching the tendons. 



Dissection (fig. 87). The fascia and the cutaneous nerves and vessels 

 are to be reflected from the muscles of the forearm, and from the tendons 

 on the back of the hand ; but in removing the fascia in the forearm, the 

 student must be careful not to cut away the posterior interosseous vessels, 

 which are in contact with it on the inner side in the lower third. A thick- 

 ened band of the fascia opposite the carpus (the posterior annular ligament) 

 is to be left. 



Let the integument be removed from the fingers, in order that the ten- 

 dons may be traced to the end of the digits. 



The several muscles should be separated from one another up to their 

 origin, especially the two radial extensors of the wrist. 



The posterior annular ligament, K, consists of the special aponeurosis 

 of the limb, thickened by the addition of some transverse fibres, and is 

 situate opposite the lower end of the bones of the forearm. This band is 

 connected at the outer part to the radius, and at the inner to the cuneiform 

 and pisiform bones. Processes from it are fixed to the bones beneath, and 



