THE COMMON CAROTID ARTERY 587 



duct, and the left recurrent laryngeal nerve. To its right side, it is in relation with the innomi- 

 nate artery, inferior thyroid veins, and remains of the thymus gland. To its left side, with the 

 left vagus nerve, left pleura, and left lung. The left subclavian artery is posterior and slightly 

 external to it. 



PLAN OF THE RELATIONS OF THE LEFT COMMON CAROTID. 

 THORACIC PORTION. 



In front. 



Sternum. 



Sternohyoid and Sternothyroid muscles. 



Left innominate vein. 



Remains of the thymus gland. 



Internally. \ Externally. 



& /TF* rv* mm \ v 



Innominate artery. I Thoracic Left vagus nerve. 



Inferior thyroid veins. \ Portion. I Left pleura and lung. 



Remains of the thymus gland. \_ _/ Left subclavian artery. 



Behind. 

 Trachea. 

 (Esophagus. 

 Thoracic duct. 

 Left recurrent laryngeal nerve. 



The cervical portions of the two common carotids resemble each other so closely 

 that one description will apply to both. Each vessel passes obliquely upward 

 from behind the sternoclavicular articulation to a level with the upper border of 

 the thyroid cartilage, opposite the fourth cervical vertebra, where it divides into 

 the external and internal carotid arteries. 



At the lower part of the neck the two common carotid arteries are separated 

 from each other by a small interval, which contains the trachea; but at the upper 

 part, the thyroid body, the larynx, and pharynx project forward between the two 

 vessels, and give the appearance of their being placed farther back in this situa- 

 tion. The common carotid artery is contained in a sheath derived from the 

 deep cervical fascia, which also encloses the internal jugular vein and vagus nerve, 

 the vein lying on the outer side of the artery, and the nerve between the artery 

 and vein, on a plane posterior to both. On opening the sheath these three struc- 

 tures are seen to be separated from one another, each being enclosed in a separate 

 fibrous investment. 



Relations. At the lower part of the neck the common carotid artery is very deeply seated, 

 being covered by the integument, superficial fascia, Platysma, and deep cervical fascia, the 

 Sternomastoid, Sternohyoid, and Sternothyroid muscles, and by the Omohyoid, opposite the 

 cricoid cartilage; but in the upper part of its course, near its termination, it is more superficial, 

 being covered merely by the integument, the superficial fascia, Platysma, deep cervical fascia, 

 and inner margin of the Sternomastoid, and, when the latter is drawn backward, it is seen to 

 be contained in a triangular space, bounded behind by the Sternomastoid, above by the pos- 

 terior belly of the Digastric, and below by the anterior belly of the Omohyoid. This part of 

 the artery is crossed obliquely, from within outward, by the Sternomastoid artery; it is crossed 

 also by the superior and middle thyroid veins, which terminate in the internal jugular; and, 

 descending on its sheath in front, is seen the descendens hypoglossi nerve, this filament being 

 joined by one or two branches fr.jm the cervical nerves, which cross the vessel from without 

 inward. Sometimes the descendens hypoglossi is contained within the sheath. The middle 

 thyroid vein crosses the artery about its middle, and the anterior jugu'ar vein below; the latter, 

 however, is separated from the artery by the Sternohyoid and Sternothyroid muscles. Behind, 

 the artery is separated from the transverse processes of the vertebrae by the Longus colli and 



