INTERNAL CUTANEOUS NERVES. 251 



directly into two : Its external branch passes beneath the median basilic 

 vein to the front of the forearm ; and the internal winds over the inner 

 condyle of the humerus to the back of the forearm. 



A cutaneous offset of the nerve pierces the fascia near the axilla, and 

 reaches as far, or nearly as far as the elbow : it supplies the integuments 

 over the inner part of the biceps muscle. 



The small internal cutaneous nerve (Wrisberg) appears below the pre- 

 ceding, and extends to the interval between the olecranon and the inner 

 condyle of the humerus, where it ends in filaments over the back of the 

 olecranon. The nerve give offsets to the lower third of the arm on the 

 inner and posterior surfaces, and joins above the elbow the inner branch 

 of the larger internal cutaneous nerve. 



The internal cutaneous branch of the musculo-spiral nerve becoming 

 subcutaneous in the upper third, winds to the back of the arm, and reaches 

 nearly as far as the olecranon. 



The intercosto-humeral branch of the second intercostal nerve (p. 22G), 

 perforates the fascia near the axilla, and ramifies in the inner side and 

 posterior surface of the arm in the upper half. But the size and distribu- 

 tion of the nerve will depend upon the development of the small internal 

 cutaneous and the offsets of the musculo-spiral. 



The aponeurosis of the arm is a white shining membrane which sur- 

 rounds the limb, and sends inwards processes between the muscle. Over 

 the biceps muscle it is thinner than elsewhere. At certain points it re- 

 ceives accessory fibres from the subjacent tendons : thus in front of the 

 elbow an offset from the tendon of the biceps joins it ; and near the axilla 

 the tendons of the pectoralis major, latissimus dorsi, and teres, send pro- 

 longations to it. 



At the upper part of the limb the fascia is continuous with that of the 

 axilla, and is prolonged over the deltoid and pectoral muscles to the scapula 

 and the clavicle. Inferiorly it is continued to the forearm, and is con- 

 nected to the prominences of bone around the elbow joint, especially to the 

 condyloid ridges of the humerus so as to give rise to the intermuscular 

 septa of the arm. 



Directions. As the back of the arm will not be dissected now, the skin 

 may be replaced on it until the front has been examined. And to keep 

 in place the vessels and nerves at the upper part of the limb, these should 

 be tied together with string in their natural position to one another, and 

 fastened to the coracoid process. 



Position. The limb is still to lie on the back, but the scapula is to be 

 raised by means of a small block ; and the bladebone is to be fixed in 

 such a position as to render tense the muscles. The inner surface of the 

 arm is to be placed towards the dissector. 



Dissection. The aponeurosis is to be reflected from the front of the 

 arm by an incision along the centre, like that through the integuments ; 

 and it is to be removed on the outer side as far as the outer condyloid 

 ridge of the humerus, but on the inner side rather farther back than the 

 corresponding line, so as to lay bare part of the triceps muscle. In rais- 

 ing the fascia the knife must be carried in the direction of the fibres of 

 the biceps muscle ; and to prevent the displacement of the brachial artery 

 and its nerves, fasten them here and there with stitches. 



In front of the elbow is a hollow containing the brachial vessels: the 

 artery should be followed into it, to show its ending in the radial and 

 ulnar trunks. 



