THE NECK 119 



horizontally backwards, and sometimes almost vertically down- 

 wards ; in the latter case it may be mistaken for the internal 

 jugular vein. It usually receives the superior thyreoid, lingual, 

 and tonsillitic veins. The last two are found under cover of 

 the posterior belly of the digastric, and often open directly into 

 the internal jugular vein. Not infrequently the common facial 

 ends by joining the anterior jugular vein, which is considerably 

 increased in size in these cases. 



The Superior Thyreoid Vein generally ascends to enter the 

 common facial, but it may join the internal jugular directly by 

 crossing the common carotid artery. 



The Middle Thyreoid Vein, which appears from under cover 

 of the anterior belly of the omo-hyoid, enters the internal jugular 

 vein after piercing the anterior aspect of the carotid sheath 

 (p. 120). 



The Common Carotid Artery. On the right side, the 

 common carotid artery arises from the innominate artery behind 

 the sterno-clavicular joint ; on the left side, it arises from the 

 arch of the aorta and lies in the superior mediastinum for 

 ij inches. The course of the artery in the neck can be mapped 

 out by a line drawn from the sterno-clavicular joint to a point 

 midway between the angle of the mandible and the mastoid 

 process. Opposite the upper border of the thyreoid cartilage, 

 which lies at the level of the fourth cervical vertebra, the common 

 carotid ends by dividing into the internal and external carotid 

 arteries. As it lies in front of the carotid tubercle (p. 107), 

 the artery is crossed by the anterior belly of the omo-hyoid, 

 which is running upwards, forwards, and medially. 



Ligature of the common carotid artery above the omo-hyoid is 

 performed for congenital hydrocephalus (Stiles), or for aneurism 

 of the innominate artery. Temporary occlusion of the vessel by 

 Crile's method may be carried out in this part of its course as a 

 preliminary step to extensive operations on the mouth or throat. 

 This proceeding is dangerous in elderly people, since it may 

 induce cerebral softening (p. 120), and in these patients the 

 external carotid should be selected. The incision may be made 

 along or obliquely across the anterior border of the sterno- 

 mastoid. The skin, superficial fascia, and the platysma are 

 divided, and the investing layer of the deep cervical fascia is 

 cut through at the anterior border of the sterno-mastoid, thus 

 allowing the muscle to be retracted to the lateral side. The 

 omo-hyoid, which is now exposed, is an important landmark, 



8c 



