COMMON CAROTID ARTERIES. 357 



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

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

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

 thyroid artery ; 4, at that of the lingual ; farther uj) the vessel may he 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 5', 

 the superior thyroid artery ; 6, the facial artery passing over the base of the jaw ; 7, the 

 superficial temporal artery ; 8, the first part, S', the third pai-t of the subclavian artery ; 

 S", the subclavian vein separated from the artery by the scalenus anticus muscle ; 9, is 

 placed on the scalenus anticus muscle in the angle between the transversalis colli and 

 suprascapular branches of the thyroid axis ; 10, outer part of the suprascapular artery ; 

 10', transverse cervical branches passing into the deep surface of the trapezius ; 10", the 

 posterior scapular artery, rising directly from the third part of the subclavian artery ; 11, 

 on the scalenus anticus muscle, points to the inferior thjToid artery near the iilace where 

 tlie ascending cervical artery of the neck is given oft' ; the phrenic nerve lies on the 

 muscle to the outside of the figure at /, the suprasternal twig of the suprascapular artery 

 is shown. 



they differ materially in their place of origin, and consequently in 

 their length and position, at their commencement. On the right side 

 the carotid artery commences at the root of the neck behind the upper 

 part of the stenio- clavicular articulation, at the bifurcation of the 

 innominate artery ; but on the left side the carotid arises within the 

 thorax, from the highest part of the arch of the aorta, very near the 

 origin of the innominate artery. 



The left carotid is thus as a whole longer than the right, and its first 

 part is placed at some depth within the thorax. While within the thorax, 

 the left carotid ascends obliquely behind and at some distance from the 

 upper piece of the sternum and the muscles (sterno-hyoid and sterno- 

 thyroid) connected with that part of the bone ; it is covered in front 

 by the remains of the thymus gland, and is crossed by the left 

 innominate vein. This part of the artery lies in front of the trachea, 

 and of the oesophagus, which, at the root of the neck, deviates a little 

 to the left side ; the thoracic duct is also behind it. The left carotid 

 artery here lies between the innominate and the left subclavian arteries, 

 and the vagus nerve is to its outer side. 



In the neck the common carotid artery of either side reaches from 

 behind the sterno-clavicular articulation to the level of the upper border 

 of the thyroid cartilage, Avhere it divides into two great branches, of 

 which one is distributed to the cranium and face, and the other to the 

 brain and eye. These divisions have, from their destination, been 

 named respectively the external and inkrnal carotid arteries. 



The oblique course taken by the common carotid artery along the side 

 of the neck is indicated by a line drawn from the sterno-clavicular arti- 

 culation to a point midway between the angle of the jaw and the mastoid 

 ^irocess of the temporal bone. At the root of the neck, the arteries of 

 opposite sides are separated from each other only by a narrow interval, 

 corresponding with the width of the trachea ; but, as they ascend, they 

 are separated by a much larger interval, corresponding with the breadth 

 of the pharynx and larynx. The carotid arteries have the appearance 

 of being placed farther back at the upper than at the lower part of the 

 neck, owing to the forward projection of the larynx above. 



The common carotid artery is enclosed, together with the internal 

 jugular vein and the vagus nerve, in a common sheath, which is 

 continuous with the deep cervical fascia ; the nerve, artery and 

 vein are, however, each contained in a separate fibrous investment 



