n6 THE UPPER EXTREMITY 



stretches transversely across the fronts of the heads of the 

 metacarpal bones. These relations can only be satisfactorily 

 made out by dividing the arch and slitting the slip of fascia 

 in an upward direction. 



Fascial Compartments of the Palm. Two weak septa pro- 

 ceed into the palm from the margins of the strong intermediate 

 portion of the palmar aponeurosis. They join a layer of fascia, 

 which is spread out over the interosseous muscles and the 

 deep volar arch, and they thus subdivide the palm into 

 three fascial compartments, viz. an intermediate, containing the 

 flexor tendons, the lumbrical muscles, the superficial volar 

 arch, and the terminal branches of the median nerve; a 

 medial, enclosing the short muscles of the little finger ; and a 

 lateral, enclosing the short muscles of the thumb. 



Dissection. Raise the intermediate part of the palmar aponeurosis. 

 Divide its narrow proximal part, throw it distally, and finally remove it 

 completely. The siiperficial volar arch is the most superficial of the struc- 

 tures now exposed. Trace the ulnar artery into it, and follow the digital 

 branches which it gives off. The lig. carpi volare which binds the ulnar 

 artery to the front of the transverse carpal ligament may now be removed. 

 The median and ulnar nerves must also be dissected. The muscular 

 branches, which the median gives to the muscles of the thenar eminence, are 

 especially liable to injury. They come off in a short, stout stem, almost in 

 a line with the lower margin of the transverse carpal ligament, and at 

 once turn laterally to reach the short muscles of the thumb, to some 

 of which they are distributed. The nerve twigs to the two lateral 

 lumbricals must also be looked for. They spring from the digital 

 branches of the median which go to the lateral side of the index and to 

 the cleft between the index and middle fingers. 



In order that the digital vessels and nerves may be traced to their 

 distribution the skin must be reflected from the fingers. This can be done 

 by making an incision along the middle of each digit, and turning the 

 integument laterally and medially. As the skin is raised from the borders 

 of the different digits the cutaneous ligaments of the phalanges (Cleland) 

 will come into view. These are fibrous bands, which spring from the 

 edges of the phalanges behind the digital vessels and nerves. They 

 are inserted into the skin so as to form a strong fibrous septum on each 

 side of each finger. They retain the integument in proper position during 

 the different movements of the digits. 



Arcus Volaris Superficialis (O.T. Superficial Palmar 

 Arch). The ulnar artery, when traced into the palm, is found 

 to form the superficial volar arch an arterial arcade, which 

 lies immediately subjacent to the palmar aponeurosis. 



The ulnar artery enters the palm by passing in front of 

 the transverse carpal ligament, close to the lateral side of the 

 pisiform bone. A short distance below this it curves laterally 

 across the palm, and, near the middle of the thenar emin- 



