I094 A MANUAL OF ANATOMY 



scapular arteries, and the anterior jugular vein. At the root of the 

 neck the nerve/ having left the scalenus anticus, passes behind the 

 terminal part of the subclavian vein, and crosses over the internal 

 mammary artery from without inwards. Having come into con- 

 tact with the inner surface of the dome of the pleura, it disappears 

 behind the inner end of the clavicle, and enters upon the thoracic 

 part of its course (see p, 942). 



The right nerve at the root of the neck is superficial to the second 

 part of the right subclavian artery, with the intervention of the 

 scalenus anticus muscle. The left nerve at the root of the neck is 

 anterior and parallel to the first part of the left subclavian artery, 

 and lies behind the terminal part of the thoracic duct. 



The phrenic nerve is sometimes reinforced towards the root of the 

 neck by a branch from the nerve to the subclavius muscle, and, 

 when this takes place, the root from the fifth cervical nerve is usually 

 absent. Before leaving the neck the phrenic nerve receives a twig 

 from the middle, or lower, cervical ganglion of the sympathetic. 



No branches arise from the phrenic nerve in the neck. 



Supraclavicular Group of Deep Cervical Glands. — These glands lie 

 in the anterior part of the supraclavicular triangle, and are related 

 superficially to the clavicular nerve, and deeply to the upper and 

 middle trunks of the brachial plexus. Superiorly they are con- 

 tinuous with the external chain of the substerno-mastoid glands. 

 They receive their afferent vessels from the following sources : 



1. The back of the neck. 



2. The external group of axillary glands. 



3. The upper part of the pectoral region. 



4. Occasionally the lymphatics along the cephalic vein, which 

 may ascend over the clavicle. 



Their efferent vessels unite, on either side, with those of the 

 internal chain of substerno-mastoid glands (superior and inferior 

 groups) to form the common jugular lymphatic trunk. 



Subclavian or Supraclavicular Triangle. — ^The subclavian triangle 

 is the lower division of the posterior triangle of the neck, and is 

 separated from the upper division, or occipital triangle, by the 

 posterior belly of the omo-hyoid muscle. It is situated above the 

 middle third of the clavicle, and is of small size until the deep cer- 

 vical fascia, which ensheathes the posterior belly of the omo-hyoid, 

 has been divided. 



Boundaries — Superior.— ^he posterior belly of the omo-hyoid 

 muscle. Inferior. — The middle third of the clavicle. Anterior. — 

 The clavicular part of the sterno-cleido-mastoid muscle. Roof. — 

 The skin ; superficial fascia and platysma myoides muscle ; supra- 

 sternal, supraclavicular, and supra-acromial nerves ; a part of the 

 external jugular vein ; and the deep cervical fascia. Floor. — ^The 

 scalenus medius and scalenus posticus muscles. 



The extent of the triangle is affected by (i) the height to which 

 the posterior belly of the omo-hyoid ascends above the clavicle, 

 and (2) the extent of the clavicular attachments of the sterno-cleido- 

 mastoid and trapezius muscles. The depth of the triangle is in- . 



