THE ANTERIOR PART OF THE NECK 235 



sterno-mastoid in the upper and posterior angle of the carotid triangle ; and 

 it also is not uncommonly hidden when the sterno-mastoid is well developed. 

 During life, however, when the muscle is soft and pliable the structures 

 concealed by it are readily exposed, for the muscle is easily displaced 

 posteriorly after the fascia has been divided along its anterior border. In 

 the dissecting-room it is not possible to obtain a proper view of the course 

 and relations of the common carotid artery and the internal jugular vein, or 

 to appreciate the relations of the first part of the subclavian artery and the 

 relations of the scalenus anterior muscle, until the sterno-mastoid has 

 been reflected. Divide the external jugular vein immediately below the 

 point where it is joined by the posterior auricular tributary and turn it 

 downwards. Divide the great auricular nerve at the level of the angle of 

 the mandible and turn it posteriorly ; and turn posteriorly 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 exposed ; 

 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. 



Deep 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 

 thyreoid gland and a short distance above the sternum. At 

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

 layer; (2) a pretracheal layer ; (3) a prevertebral layer; and (4) 

 a fascial 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 posteriorly, splits to enclose the sterno-mastoid 

 muscle. Beyond the sterno-mastoid it passes posteriorly 

 to the anterior border of the trapezius muscle, forming the 

 roof of the posterior triangle, then splits again to enclose the 

 trapezius, along the surfaces of which it is prolonged till it 

 blends with the supraspinous ligaments and the ligamentum 



