1360 CLINICAL AND TOPOGRAPHICAL ANATOMY 



The accessory nerve, having crossed the transverse process of the atlas at a 

 point lying a little below and in front of the apex of the mastoid, enters the ante- 

 rior border of the sterno-mastoid at about the junction of the upper and middle 

 thirds of the muscle. Having traversed the muscle obliquely, it leaves it usually 

 at a point a little lower down, pursues a similar course across the posterior triangle 

 and disappears under the anterior border of the trapezius, to enter into the sub- 

 trapezial plexus with the third and fourth cervical nerves. 



Above it is accompanied by a branch from the occipital, below by the transverse cervical 

 artery. It is always seen in thorough operations on the upper deep cervical glands. The nerve 

 is resected in spasmodic torticollis, and in recent years inveterate facial paralysis has been 

 treated by anastomosing the facial to this nerve or the hypoglossal. A line drawn from midway 

 between the tip of the mastoid and the angle of the mandible along the above given course of 

 the nerve would denote its position. 



Just above the centre of the sterno-mastoid, the small occipital, great auricular, and cuta- 

 neous cervical nerves emerge, the first passing upward and backward to the scalp, the second 

 upward and forward across the upper part of the sterno-mastoid to the ear, and the last turning 

 straight forward to the front of the neck. The small occipital and great auricular are often 

 in intimate association with the accessory at its exit from the muscle. At this point also care 

 must be taken not to injure the nerve in removal of glands from the posterior triangle. 



The phrenic nerve, taking its largest root from the fourth cervical, would 

 begin deeply about the level of the hyoid bone; thence descending under the 

 sterno-mastoid, and, passing obliquely medially across the scalenus anterior (the 

 posterior borders of the above two muscles roughly correspond to each other in 

 the lower part of the neck), it descends under the subclavian vein and clavicle to 

 enter the thorax. 



When the internal j ugular is distended, its lateral border will be liable to overlap this nerve. 

 The relations of the scalenus anterior should be noted here. In addition to the phrenic, which 

 runs with a slight obliquity medially and is in close contact with the muscle, the following struc- 

 tures cross it medio-laterally: the subclavian vein and termination of the external jugular, 

 the transverse scapular and transverse cervical vessels, and the omo-hyoid. At its medial 

 margin are the thyreo-cervical trunk and vertebral arteries, and over them, the internal jugular. 

 Behind it are the subclavian artery, the brachial plexus, and pleura. 



The level of the brachial plexus (upper border) would be given by a Hne drawn 

 from the cricoid cartilage to the centre of the clavicle. The lowest, medial cord 

 (eighth cervical and first thoracic, giving off chiefly the ulnar, medial head of 

 median, and medial antibrachial cutaneous) is just above and behind the sub- 

 clavian artery. Its importance in ligature of the artery has been referred to 

 (p. 1359). 



In paralys's of the newly born, after some violent manipulation, it is usually the upper and 

 lateral cord (fifth nerve, and axillary and median chiefly) which suffers, elevation and abduction 

 at the shoulder and flexion at the elbow-joint being lost. 



Collateral circulation after ligature of the common carotid (fig. 1102).— This takes place 

 by means of (1) the free communication which exists between the opposite carotids, both with- 

 out and within the craniu;n; and (2) by enlargement of the branches of the subclavian artery on 

 the same side as that on which the carotid has been tied. Thus, outside the cranium, the supe- 

 rior and inferior thyreoids are the chief vessels employed (fig. 1102). Within the cranium the 

 vertei)ral replaces the internal carotid. 



Collateral circulation after ligature of the second and third parts of the subclavian (fig. 1102). 

 — Here the following three sets of vessels are those chiefly employed: — 



The transverse scapular, the transverse \ ^y[tu i i'hG thoraco-acromial, infra- and sub- 

 cervical, I 1 scapular, and circumflex scapular. 



The superior intercostal, the aortic inter- 1 •. i f The lateral thoracic and subscapular 



costals, and the internal mammary, j \ arteries. 



Numerous unnamed l)ranchcs passing ] 



through the axilla from branches of the [ with Branches of the axillary, 

 subclavian, J 



Deep cervical fascia. — The arrangement of this must be remembered — (a) 

 above, and (h) l)elo\v, the hyoid bone. The latter is far more important. 



(a) Arrangement above the hyoid bone. — Here two chief processes can be made out: — (i) 

 one, continuous with that in front of the sterno-mastoid, traced upward from the hyoid bone, 

 ciiclos(!s the submaxillary gland, passing over the inylo-hyoid, and, ascending, is connected with 

 the lower border oi the mandible, gives oi'f t-lic inassctcric and parotid fascia;, and is attached 

 to the lower border of the zygoma, and, more posteriorly, to the mastoid and linea nuchse 

 suprcma. (ii) A spe';ial process, which forms the stylo-maiidibuhir ligament, is important in 

 its power of chocking over-action of the external |)tcrygoid. liy both these processes the ante- 

 rior border of the sterno-mastoid is tied firmly forward to the mandible about its angle, and more 

 deeply to the styloid process. Thi.s renders all oj)crations under the upper part of the muscle, 

 e. g., the removal of glands, extremely difficult. 



