THE BRACHIAL PLEXUS 55 



suprascapular). Below the clavicle it is covered by the skin 

 and superficial fascia, the platysrna, the middle supraclavicular 

 nerves, the deep fascia, the pectoralis major, the pectoralis 

 minor, the cephalic vein, the branches of the thoraco-acromial 

 artery, the costo-coracoid membrane, and the axillary artery 

 and vein (Figs. 15, 16, 49, 51). 



Its posterior relations in the neck are the scalenus medius 

 and the long thoracic nerve. Its posterior relations in the 

 axilla are the serratus anterior, the fat in the interval between 

 the serratus anterior and the subscapularis, and, finally, the 

 subscapularis itself. 



After the brachial plexus has been examined, the clavicle 

 must be replaced in position and the skin flap, reflected from 

 the posterior triangle, must be replaced and fixed in position 

 by a few sutures. 



On the ninth day after the body is brought into the room, 

 that is, on the sixth day after it has been placed on its back, 

 it will be turned upon its face, with the thorax and the pelvis 

 supported by blocks. The body will remain upon its face for 

 five days, and during that period the dissectors of the head 

 and neck must complete the dissection of the posterior part 

 of the scalp ; dissect the muscles, vessels and nerves of the 

 back and the sub-occipital region ; and remove and examine 

 the spinal medulla. 



THE DISSECTION OF THE BACK. 



Dissection. Make a median longitudinal incision from the 

 external occipital protuberance to the seventh cervical spine, 

 and a second incision laterally from the seventh cervical spine 

 to the acromion, and throw the flap laterally. When that has 

 been done the posterior triangle will be exposed from behind, 

 and the dissector should take the opportunity of noting the 

 positions of the contents and the constituent parts of the floor 

 from that aspect. Afterwards he must look for the superficial 

 nerves in the superficial fascia over the upper part of the trapezius. 

 If the greater occipital nerve was not found during the dissection 

 of the scalp, secure it at once, as it pierces the deep fascia covering 

 the upper end of the trapezius, about midway between the 

 external occipital protuberance and the posterior border of the 

 mastoid portion of the temporal bone ; trace it upwards through 

 the dense superficial fascia of the scalp, and clean the branches 

 of the occipital artery which are distributed in the same region. 

 The third occipital nerve will be found in the superficial fascia 

 between the greater occipital and the median plane. It is the 

 medial division of the posterior ramus of the third cervical nerve, 

 in 4 b 



