42 HEAD AND NECK 



lower and lateral part is behind the clavicle. The part in 

 the triangle is situated deeply in the anterior inferior angle, 

 and below the omo-hyoid muscle. It lies deep to the skin, 

 superficial fascia, the platysma, deep fascia, the external 

 jugular vein, the ends of the transverse scapular and trans- 

 verse cervical veins, and the nerve to the subclavius muscle. 

 The lowest trunk of the brachial plexus is behind it and 

 separates it from the insertion of the scalenus medius. Below^ 

 it rests upon the first rib, against which it can be compressed, 

 and, more medially, upon the cervical pleura. 



The Brachial Plexus and its Supraclavicular Branches. 

 Only the upper portion of the brachial plexus lies in the 

 region of the posterior triangle, i.e. the roots, the trunks, and 

 some of the branches ; the remainder lies either posterior to 

 the clavicle or in the axilla. The cervical portion lies in the 

 lower and anterior part of the posterior triangle, partly in the 

 occipital and partly in the supraclavicular areas. The detailed 

 study of the plexus should be left till the fifth day after the 

 body has been placed upon its back, when the dissector of 

 the head and neck will assist the dissector of the upper 

 extremity to disarticulate the clavicle and to lay bare the 

 whole of the plexus (p. 36); but it should be noted now 

 (i) that the cervical part of the plexus lies deep to the skin, 

 superficial fascia, platysma and deep fascia, and that it is 

 crossed superficially by the posterior belly of the omo-hyoid 

 muscle, the external jugular vein, the transverse cervical 

 artery and the transverse cervical and transverse scapular 

 veins; (2) that part of the third portion of the subclavian 

 artery is superficial to the lower part of the plexus ; and 

 (3) that behind the plexus is the lower part of the scalenus 

 medius muscle. 



The fourth day after the body has been placed upon its 

 back should be devoted to the study of the temporal region 

 and the scalp. 



THE SCALP AND THE SUPERFICIAL STRUCTURES 

 OF THE TEMPORAL REGION. 



Under the term " scalp " are included the soft structures 

 which cover the vault of the cranium above the temporal 

 lines and anterior to the superior nuchal line. Its con- 



