io8 THE HEAD AND NECK 



spines lie at the bottom of the nuchal furrow, and are obscured 

 by the ligamentum nuchae. 



The Platysma. This muscular sheet lies in the superficial 

 fascia of the neck. Its anterior border runs obliquely upwards 

 and medially. For a short distance below the chin it meets 

 and decussates with the corresponding muscle of the opposite 

 side, but the two muscles separate from one another below 

 (Fig. 51). It is supplied on its deep surface by the cervical 

 branch of the facial nerve. The platysma aids the facial muscles 

 which drag downwards the lower lip and the angle of the mouth. 

 Incisions which approach too near to the angle of the mandible 

 (p. 134) may cut the nerve to the platysma (and depressor labii 

 inf.) and cause paralysis of the movements indicated. 



Superficial Nerves. The skin of the front and side of the 

 neck is supplied by branches from C. 2, C. 3, and C. 4. The 

 nerves appear from under cover of the sterno-mastoid, near 

 the middle of its posterior border, and radiate in various direc- 

 tions. Like the superficial veins, they lie deep to the platysma. 



The descending, supra-clavicular, branches (C. 3 and C. 4) 

 are described on p. 4. 



The ascending branches are the lesser occipital (C. 2), which 

 runs upwards along the posterior border of the sterno-mastoid 

 to the scalp, and the great auricular (C. 2 and 3), which ascends 

 across the muscle superficially, and supplies the skin over the 

 angle of the jaw and the postero-inferior part of the auricle. 

 The great auricular nerve usually accompanies the upper half 

 of the external jugular vein (Fig. 35). 



These nerves are commonly divided in operations for the 

 removal of tuberculous lymph glands, and occasionally their 

 cut ends become adherent to the scar. Neuralgia, arising 

 from this cause, radiates over the area supplied by the other 

 nerves which arise from the same segment of the spinal medulla 

 as the nerve involved. The surgeon may resect the superficial 

 nerves of the neck as soon as they are exposed as a prophylactic 

 measure, and, although some loss of sensation may result, the 

 condition gradually improves. 



Posteriorly, the skin is supplied by the posterior rami (primary 

 divisions) of the second to the sixth cervical nerves. 



The line of anaesthesia in fracture dislocations below the 

 fourth cervical vertebra is described on p. 530. 



The External Jugular Vein is formed at the lower border of 

 the parotid gland by the union of the posterior auricular and a 



