

I 





THE COMMON CAROTID ARTERY 549 



to it is the trachea, which it crosses obliquely. On the right side are the right innominate vein, 

 the superior vena cava, the right phrenic nerve, and the pleura; and on the left side, the remains 

 of the thymus, the origin of the left common carotid artery, the inferior thyroid veins, and the 

 trachea. 



Branches. The innominate artery usually gives off no branches; but occasion- 

 ally a small branch, the thyreoidea ima, arises from it. Sometimes it gives off a 

 thymic or bronchial branch. 



The thyreoidea ima (a. thyreoidea ima) ascends in front of the trachea to the 

 lower part of the thyroid gland, which it supplies. It varies greatly in size, and 

 appears to compensate for deficiency or absence of one of the other thyroid 

 vessels. It occasionally arises from the aorta, the right common carotid, the 

 subclavian or the internal mammary. 



Point of Division. The innominate artery sometimes divides above the level of the sterno- 

 clavicular joint, less frequently below it. 



Position. When the aortic arch is on the right side, the innominate is directed to the left side 

 of the neck. 



Collateral Circulation. Allan Burns demonstrated, on the dead subject, the possibility of the 

 establishment of the collateral circulation after ligature of the innominate artery, by tying and 

 dividing that artery. He then found that "Even coarse injection, impelled into the aorta, passed 

 freely by the anastomosing branches into the arteries of the right arm, filling them and all the 

 vessels of the head completely." 1 The branches by which this circulation would be carried on 

 are very numerous; thus, all the communications across the middle line between the branches 

 of the carotid arteries of opposite sides would be available for the supply of blood to the right 

 side of the head and neck; while the anastomosis between the costocervical of the subclavian and 

 the first aortic intercostal (see infra on the collateral circulation after obliteration of the thoracic 

 aorta) would bring the blood, by a free and direct course, into the right subclavian. The numerous 

 connections, also, between the intercostal arteries and the branches of the axillary and internal 

 mammary arteries would, doubtless, assist in the supply of blood to the right arm, while the 

 inferior epigastric from the external iliac would, by means of its anastomosis with the internal 

 mammary, compensate for any deficiency in the vascularity of the wall of the chest. 



THE ARTERIES OF THE HEAD AND NECK. 



The principal arteries of supply to the head and neck are the two common 

 carotids; they ascend in the neck and each divides into two branches, viz., (1) the 

 external carotid, supplying the exterior of the head, the face, and the greater part 

 of the neck; (2) the internal carotid, supplying to a great extent the parts within 

 the cranial and orbital cavities. 



Tl 



rinlii 



THE COMMON CAROTID ARTERY (A. CAROTIS COMMUNIS). 



The common carotid arteries differ in length and in their mode of origin. The 

 right begins at the bifurcation of the innominate artery behind the sternoclavicular 

 joint and is confined to the neck. The left springs from the highest part of the 

 arch of the aorta to the left of, and on a plane posterior to the innominate artery, 

 and therefore consists of a thoracic and a cervical portion. 



The thoracic portion of the left common carotid artery ascends from the arch of 

 the aorta through the superior mediastinum to the level of the left sternoclavicular 

 joint, where it is continuous with the cervical portion. 



Relations. In front, it is separated from the manubrium sterni by the Sternohyoideus and 

 Sternothyreoideus, the anterior portions of the left pleura and lung, the left innominate vein, 

 and the remains of the thymus; behind, it lies on the trachea, esophagus, left recurrent nerve, 

 and thoracic duct. To its right side below is the innominate artery, and above, the trachea, the 

 inferior thyroid veins, and the remains of the thymus; to its left side are the left vagus and phrenic 

 nerves, left pleura, and lung. The left subclavian artery is posterior and slightly lateral to it. 



1 Surgical Anatomy of fie Head and Neck, p. 62. 



