THE ANTERIOR PART OF THE NECK 135 



the union of the posterior auricular vein with the communication 

 from the posterior facial vein, and turn it downwards. Divide 

 the great auricular nerve at the level of the angle of the mandible 

 and turn it backwards ; and turn backwards also the nervus 

 cutaneus colli, whose two terminal branches have been cut 

 already. The clavicular head of the sterno-mastoid was cut 

 when the clavicle was removed ; now divide the sternal head, 

 turn the muscle upwards towards its insertion. As the muscle is 

 turned upwards, sterno-mastoid branches of the transverse 

 scapular, superior thyreoid, and occipital arteries will be ex- 

 posed ; and if they interfere with the reflection of the muscle 

 they must be divided. Slightly above the level of the sterno- 

 mastoid branch of the occipital artery the accessory nerve will 

 be found passing through the deeper fibres of the muscle, and 

 care must be taken to avoid injury to it ; but it may be dissected 

 out of the muscle and left in position on the lateral surface of 

 the internal jugular vein. 



eep Cervical Fascia. When the sterno-mastoid has been 

 reflected, a deep fascial plane of the neck is exposed in which 

 lie many lymph glands. Before carrying the dissection further 

 the dissector should reconsider the arrangement of the deep 

 cervical fascia. He has already seen that it forms a complete 

 sheath enclosing the muscles of the neck and the structures 

 ^ which lie between and under cover of them. The general 

 *^ arrangement of the fascia is studied best on transverse 

 ^ sections of the neck made at the level of the isthmus of the 

 r^ thyreoid gland and a short distance above the sternum. At 

 1^ the former level it is possible to recognise (i) a superficial 

 *^Javer; (2) a pretracheal layer; (3) a prevertebral layer; and (4) 

 L. ara-scial sheath which encloses the common carotid arteries, 

 the internal jugular vein and the vagus nerve, as they lie in 

 the angular interval between the sterno-mastoid laterally, the 

 thyreoid gland, the trachea, oesophagus medially, and the 

 prevertebral muscles posteriorly. 



The first or superficial layer, as it is traced backwards, 

 splits to enclose the sterno-mastoid muscle (Fig. 47). Beyond 

 the sterno-mastoid it passes backwards to the anterior border 

 of the trapezius muscle, forming the roof of the posterior 

 triangle; then it splits again to enclose the trapezius, along 

 the surfaces of which it is prolonged till it blends with the 

 supraspinous ligaments and the ligamentum nuchae. The 

 lamella which covers the deep surface of the sterno-mastoid is 

 blended with the lateral surface of the carotid sheath. The 

 pretracheal layer, which has been dissected already in the 

 median plane, ensheaths the thyreoid gland and blends 

 in 96 



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