n6 THE HEAD AND NECK 



Within the carotid sheath lie the common carotid and the 

 commencement of the internal carotid artery, the internal jugular 

 vein, the vagus nerve, and some lymph glands. The artery 

 is situated medially and on a plane somewhat anterior to the 

 internal jugular vein, but it is overlapped by the vein, which is 

 considerably the larger of the two vessels. The vagus nerve 

 lies between and behind the artery and the vein. The ramus 

 descendens hypoglossi (p. 154) is embedded in the anterior aspect 

 of the sheath. 



(e) The Stylo-mandibular Ligament connects the styloid 

 process to the deep surface of the angle of the mandible. It 

 forms a part of the sheath of the parotid gland, and it separates 

 the parotid from the submaxillary region. 



The Sterno-mastoid Muscle arises by a sternal and a 

 clavicular head, separated from one another by a triangular 

 interval, in the floor of which lies the lower end of the carotid 

 sheath. The fibres of the muscle pass upwards and backwards 

 to the mastoid process and the superior nuchal line of the 

 occipital bone. The muscle is firmly held in place by the deep 

 fascia, and its anterior border shows a forward convexity 

 which disappears when the fascia is incised along it, permitting 

 the carotid sheath to come into view. The nerve-supply of the 

 sterno-mastoid is derived from the accessory (spinal accessory) 

 nerve and the anterior ramus (primary division) of C. 2. When 

 the accessory nerve is cut, the muscle of the opposite side, being 

 unopposed, draws the head down to its own side, and at the same 

 time rotates and tilts the head so that the chin is directed up- 

 wards and towards the affected side. In these cases, therefore, 

 the torti-collis is found on the other side of the neck from the 

 causative lesion. Congenital torti-collis is due to shortening of 

 the muscle of the same side, either from mal-development or 

 from cicatricial fibrosis following rupture during parturition. 



Acquired torti-collis may be due to astigmatism, or to the 

 irritation of the second cervical nerve by Potts' disease, or it may 

 be caused by the pressure of inflamed lymph glands on the 

 accessory nerve. This variety can always be distinguished from 

 the true form by the absence of facial asymmetry. 



In the treatment of congenital torti-collis, subcutaneous 

 tenotomy of the sterno-mastoid near its origin has fallen into 

 disuse on account of the danger of wounding the anterior or the 

 external jugular vein (p. 108). In addition, the deep cervical 

 fascia, which is also contracted, must be divided in order to 



