98 THE SUPERIOR EXTREMITY 



to the distal part of the arm, both on the anterior and 

 posterior aspects, and then descends to supply the skin 

 of the middle of the back of the forearm as far as the 

 wrist (Figs. 31, 32). 



The lateral cutaneous nerve of the forearm pierces the deep 

 fascia proximal to the elbow, passes deep to the cephalic 

 vein, and supplies the skin on the lateral parts of the volar 

 and dorsal aspects of the forearm as far as the wrist. It 

 also supplies the skin of the proximal part of the thenar 

 eminence (Figs. 31, 32). 



Fascia Brachii. After the cutaneous nerves have been 

 revised re-examine the deep fascia of the arm. Note (i) 

 that it consists largely of transverse fibres ; (2) its close 

 attachment to the bony prominences at the elbow and 

 to the distal parts of the medial and lateral borders 

 of the humerus ; (3) its connection with the muscles 

 which spring from the medial and lateral epicondyles of the 

 humerus ; (4) the thickened band of fibres called the lacertus 

 fibrosus which passes from the distal part of the medial 

 border of the biceps to the medial side of the proximal 

 part of the forearm (Figs. 31, 61). It is also connected 

 with the tendons of insertion of the deltoid, the pectoralis 

 major and the latissimus dorsi, but those connections were 

 severed when the muscles were cleaned. 



Dissection. (i) Cut through the deep fascia along the 

 proximal and distal borders of the lacertus fibrosus, from the 

 medial margin of the biceps to the medial margin of the fore- 

 arm, and leave the lacertus fibrosus in position when the re- 

 mainder of the deep fascia is reflected. (2) Make a longitudinal 

 incision through the deep fascia along the middle line of the 

 biceps. (3) At the level of the epicondyles make a transverse 

 incision through each of the flaps marked out by the longitudinal 

 incision, and (4) reflect each of the two flaps to its own side. 

 As the reflection proceeds it will become evident that septa pass 

 from the deep surface of the deep fascia between the various 

 muscles. Thus a septum passes transversely from side to side 

 between the biceps and brachialis muscles (Figs. 42, 43). In it 

 is embedded the musculo-cutaneous nerve. A septum dips back- 

 wards between the brachialis and the muscles which spring from 

 the anterior lip of the distal half of the lateral border of the 

 humerus. The radial nerve and anterior branch of the pro- 

 funda artery are embedded in it (Fig. 42), but the strongest 

 and most important septa are the lateral and medial inter- 

 muscular septa which separate the structures at the back of the 

 arm from those at the front. Each is attached to the whole 

 length of the corresponding border of the body of the humerus, 

 but the distal halves are the strongest parts. The medial inter- 



