32 HEAD AND NECK 



POSTERIOR TRIANGLE. 



Dissection. To expose the boundaries and contents of the 

 posterior triangle make the following three incisions through 

 the skin, (i) From the back of the auricle, along the upper 

 border of the mastoid part of the temporal bone and the superior 

 nuchal line to the external occipital protuberance. (2) From 

 the sternal to the acromial end of the clavicle, following the line 

 of that bone. (3) Join the anterior extremities of I and 2 by 

 an incision, passing along the back of the external acoustic 

 meatus, and then down the middle of the sterno-mastoid muscle. 

 Reflect the flap, thus marked out, from before backwards, and 

 note that the skin is thicker over the upper and posterior part 

 of the triangle than over the lower and anterior part. 



When the skin is reflected the superficial fascia and the 

 lower part of the platysma muscle will be exposed. 



The superficial fascia in the region of the posterior triangle 

 is comparatively thin, and embedded in its lower and anterior 

 part is the lower and posterior part of the platysma. 



M. Platysma. The platysma is a thin sheet of muscle 

 which commences in the superficial fascia of the infra-clavicu- 

 lar region, whence it ascends, across the clavicle and through 

 the superficial fascia of the side of the neck, to the face, where 

 its upper border has been examined already (p. 7). It 

 covers the lower and anterior part of the posterior triangle, 

 and the upper and posterior part of the anterior triangle ; and 

 it is supplied by the cervical branch of the facial nerve, 

 which emerges from the lower end of the parotid gland. 



Dissection. Make an incision through the lower part of the 

 platysma along the line of the clavicle, and turn the part above 

 the incision upwards and forwards. Whilst making the incision 

 and ^whilst reflecting the muscle, be careful not to injure the 

 supra-clavicular cutaneous nerves and the external jugular 

 vein, which lie directly subjacent to the platysma. 



After the platysma is reflected, clean the external jugular 

 vein, which commences at the lower end of the parotid gland, 

 and passes downwards, inclining backwards, to the lower and 

 anterior angle of the posterior triangle, where it pierces the deep 

 fascia. (See pp. 34, 40, and Figs, n and 15.) Whilst clean- 

 ing the vein, avoid injury to the nervus cutaneus colli, which 

 sometimes crosses superficial to the vein about the middle of 

 its length. Secure and clean the posterior auricular vein, which 

 descends behind the auricle and joins the external jugular a little 

 below the level of the angle of the mandible. Next, find and 

 clean the superficial branches of the cervical plexus as they 

 pierce the deep fascia. They are : (i) Descending branches, 

 the anterior, middle, and posterior supra-clavicular nerves. 

 (2) A transverse branch, the nervus cutaneus colli (O.T. trans- 

 verse cervical). (3) Ascending branches, the great auricular 

 and the lesser occipital (Figs, n, 15). 



