70 THE SUPERIOR EXTREMITY 



the biceps under cover of the cephalic vein, about 25 mm. 

 above the point where the medial cubital vein leaves the cephalic 

 vein. Soon after it enters the superficial fascia it divides into 

 a volar and a dorsal branch. The volar branch descends along 

 the radial part of the volar aspect of the forearm to the ball of the 

 thumb, and the dorsal branch may be traced distally on the dorsal 

 aspect of the radial side of the forearm as far as the wrist. 



The posterior cutaneous nerve of the arm was found during 

 the dissection of the axilla springing from the proximal part of 

 the radial nerve. Now it must be traced along the dorsal aspect 

 of the arm to the elbow. It supplies the skin of the dorsum of 

 the arm from the axilla to the elbow (Fig. 32). 



After the posterior cutaneous nerve of the arm has been 

 cleaned, place the limb on its dorsal surface and look for the 

 palmar cutaneous branches of the median and ulnar nerves. 



They both pierce the deep fascia of the forearm about 30 

 mm. proximal to the wrist. The palmar cutaneous branch of 

 the median nerve lies in the line of the medial border of the 

 proximal end of the ball of the thumb (thenar eminence) and it 

 extends to the middle of the palm. The palmar cutaneous 

 branch of the ulnar nerve lies in the line of the middle of the 

 ball of the little finger (hypothenar eminence) ; it also extends to 

 the level of the middle of the palm (Fig. 31). 



After the distribution of the palmar cutaneous nerves has 

 been seen clear away the superficial fascia of the palm from the 

 interval between the thenar and hypothenar eminences to the 

 bases of the digits to expose the intermediate part of the palmar 

 aponeurosis, that is, the deep fascia of the palm. Note that the 

 superficial fascia in the area under consideration is dense. It is 

 divided into small lobules by fibrous septa which pass from the 

 skin to the palmar aponeurosis. When the intermediate part of 

 the palmar aponeurosis is exposed it will be found to be triangular 

 in outline. The apex lies at the wrist where it is continuous with 

 the deep fascia of the forearm. The base is at the level of the 

 distal ends of the metacarpal bones, and it divides into five pieces, 

 one for each finger and a less definite slip for the thumb. A 

 bundle of transverse fibres will be met with in the fold of skin 

 which crosses the proximal ends of the interdigital clefts. It is 

 the superficial transverse ligament of the hand, and it must be 

 divided opposite the clefts in order that the volar digital nerves 

 which supply the adjacent sides of the clefts may be followed. 



The volar digital nerves are seven in number. The first and 

 second pass to the thumb, one to its radial and one to its ulnar 

 side. They are accompanied by branches of the princeps pollicis 

 artery. They will be found at the medial margin of the thenar 

 eminence and must be traced to the end of the thumb. The third 

 appears at the lateral margin of the slip of the palmar aponeurosis 

 to the index-finger. It runs along the radial side of the finger 

 accompanied by the volar radialis indicis artery. The fourth, 

 fifth, and sixth will be found between the slips of the inter- 

 mediate part of the palmar aponeurosis in line with the first, 

 second, and third interdigital clefts respectively. Each is ac- 

 companied by a volar digital artery, and like the artery it divides 

 to supply the adjacent sides of the fingers which bound the cleft 

 opposite which it lies. The seventh supplies the ulnar side of 

 the little finger. It appears at the distal border of the palmaris 



