RELATIONS OF THE COMMON CAROTIDS. 343 



longus colli muscle, pointing to the pneuraogastric nerve ; IV, the uppermost of the nerves 

 of the axillary plexus ; A, the innominate artery ; 1, right common carotid artery ; 

 1', placed on the left sterno-thyroid muscle, points to a part of the left common carotid ; 

 2, internal carotid ; 2', upper part of the internal jugular vein, which has been removed 

 between i, and 2'; 3, and 4, external carotid ; 3, is placed at the origin of the superior 

 thyroid artery ; 4, at that of the lingual ; farther up the vessel may be seen the separa- 

 tion of the sterno-mastoid twig and the facial and occipital branches from the main vessel ; 

 5, is placed on the thyro-hyoid muscle between the hyoid and laryngeal branches of 

 the superior thyroid artery ; 5', the thyroid or glandular ; 6, the facial artery passing 

 over the base of the jaw ; 7, the superficial temporal artery ; 8, the first part, 8', the 

 third part of the arch of the subclavian artery ; 8", the subclavian vein separated from 

 the artery by the scalenus anticus muscle, shown by the removal of a portion of the 

 clavicle ; 9, is placed on the scalenus anticus muscle in the angle between the trans- 

 versalis colli and suprascapular branches of the thyroid axis ; 10, outer part of the supra- 

 scapular artery ; 10', transverse cervical branches passing into the deep surface of the 

 trapezius ; 10", the posterior scapular artery, represented as rising directly from the 

 third part of the subclavian artery, and passing through the axillary plexus of nerves 

 and under the levator auguli scapulae ; 11, on the scalenus anticus muscle, points to the 

 inferior thyroid artery near the place where the ascending muscular artery of the neck is 

 piven off; the phrenic nerve lies on the muscle to the outside ; at i, the suprasterual 

 twig of the suprascapular artery is shown. 



Posteriorly, the artery is supported by the cervical vertebrae, the longus 

 colli and rectus capitis anticus muscles intervening. Hence the flow of 

 blood through it may be commanded by pressure directed backwards against 

 the vertebral column. The inferior thyroid artery crosses behind the 

 carotid sheath. 



On the inner side the vessel is in juxtaposition with the trachea below, 

 and with the thyroid body (which often overlaps the artery), the larynx, 

 and the pharynx higher up. Along its outer side are placed the internal 

 jugular vein and the vagus nerve. 



Relation to Veins. The internal jugular vein is close to the artery at the 

 upper part of the neck, but, in approaching the thorax, the veins of both 

 sides incline to the right, and hence that of the right side is separated from 

 the artery by an angular interval, while that of the left side approaches the 

 artery, and even lies in front of it at the lower part of the neck. 



Crossing over the upper part of the common carotid artery to join with 

 the jugular vein, are two or more superior thyroid veins, which occasionally 

 form a sort of plexus over the artery. A middle thyroid vein not unfrequently 

 crosses the artery about half way up the neck. 



The anterior jugular vein, where it turns outwards under the sterno- 

 mastoid muscle to join the subclavian, crosses the lower part of the artery. 

 This vein is generally of small size, but occasionally is rather large, and is 

 placed nearly over the carotid artery along the neck. 



Relation to Nerves. The descending branch of the hypoglossal nerve, 

 descendens noni, usually rests, together with the branches of cervical nerves 

 which join it, on the fore part of the sheath of the carotid artery, and 

 crosses it from the outer to the inner side : in some instances this branch 

 descends within the sheath between the carotid artery and jugular vein. 

 The vagus nerve lies within the sheath of the vessels between the artery and 

 vein posteriorly : it was in one case observed to descend over the artery. 

 The sympathetic nerve is placed along the back of the sheath, between it and 

 the vertebral muscles, and the recurrent laryngeal nerve crosses inwards 

 behind the upper part of the sheath. 



The common carotid artery usually gives off no branch, and therefore 

 continues of equal size in its whole length, except at its bifurcation, where 

 a slight enlargement is observable. 



