A 



MANUAL OF ANATOMY 



PART I 



v 



THE HEAD AND NECK 



THE platysma myoides is a thin sheet of striated fibres between the 

 two layers of the superficial fascia. It arises from the fasciae of the 

 deltoid and pectoral regions, and is inserted into the bocjy of the lower 

 jaw and with the muscles at the commissure of the lips. Thus its 

 action is to depress the jaw and to draw down the corner of the mouth. 

 Being a muscle of (unhappy) expression, its nerve-supply is from (the 

 lower division of) the facial ; it also receives twigs from the superficial 

 cervical. 



Relations. Beneath it are the anterior and external jugular veins, 

 the superficial branches of the cervical plexus, and the infra-maxillary 

 nerve ; the deep fasciae ; deltoid, clavicle, pectoralis major ; sterno- 

 mastoid ; masseter ; facial vessels, and buccinator. 



Passing from the shoulder towards the jaw, the line of the fibres 

 of the muscle is that of the external jugular vein, which is readily 

 seen through the thin muscle. When bleeding from this vein, the 

 surgeon must make his incision at right angles to the course of the 

 vein and across the fibres of the platysma, so that the blood may freely 

 escape through a widely open wound, and not become extravasated 

 beneath the muscle. 



THE DEEP CERVICAL FASCIA 



The deep fascia may be traced from the spinous process of the 

 seventh cervical vertebra and the ligamentum nuchag as a thin covering 

 to the trapezius ; having reached the anterior border of that muscle, it 

 is slightly reinforced by a layer from beneath it. This thickened layer 



B 



