586 THE VASCULAR SYSTEMS 



and middle thirds of the clavicle. The skin flap with the fascia and Platysma muscle is turned 

 hack. The Sternomastoid is severed close to its insertion into clavicle and sternum. The Sterno- 

 thyroid, Sternohyoid, and Omohyoid are also divided." The sternoclavicular joint and the 

 right side of the manubrium are honeycombed by means of a surgical engine or trephine. A 

 flat retractor is slid underneath the joint while the trephining is done to protect the underlying 

 parts. The block of bone is now removed. The right and left innominate veins going down 

 to form the superior vena cava, with the vagus and right recurrent laryngeal nerves resting on 

 the innominate artery, are all plainly to be seen. The sheath of the innominate artery is now 

 opened and a ligature is applied. Burrell states that the exposure which is given by the removal 

 of a part of the sternum is extremely satisfactory, and he fails to understand how a ligature 

 can be applied to the innominate artery with any safety without a clear view of the anatomical 

 structures involved. 



Peculiarities in Point of Division. When the bifurcation of the innominate artery varies 

 from the point above mentioned it sometimes ascends a considerable distance above the sternal 

 end of the clavicle; less frequently it divides below it. In the former class of cases its length 

 may exceed two inches, and in the latter be reduced to an inch or less. These are points of con- 

 siderable interest for the surgeon to remember in connection with the operation of tying this 

 vessel. 



Position. When the aorta arches over to the right side, the innominate is directed to the 

 left side of the neck instead of the right. 



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

 the establishment of the collateral circulation after ligation of the innominate artery, by tying 

 and dividing that artery, after which, he says, "Even coarse injection, impelled into the aorta, 

 passes freely by the anastomosing branches into the arteries of the right arm, rilling 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 anastomosis between the superior intercostal of 

 the subclavian and the first- aortic intercostal (see infra on the collateral circulation after oblitera- 

 tion 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 deep epigastric, from the external iliac, would, by means of its anasto- 

 mosis with the internal mammary, compensate for any deficiency in the va.scularity of the wall 

 of the thorax. 



ARTERIES OF THE HEAD AND NECK. 



The chief artery which supplies the head and neck on each side is the common 

 carotid; it ascends in the neck and divides into two branches: (1) The external 

 carotid, supplying the superficial parts of the head and face and the greater part 

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

 the cranial cavity. 



THE COMMON CAROTID ARTERY (A. CAROTIS COMMUNIS) (Figs. 431, 432). 



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

 right common carotid (a. carotis communis dextra) begins at the bifurcation of the 

 innominate artery, behind the right sternoclavicular articulation, and is confined 

 to the neck. The left common carotid (a. carotis communis sinistra} arises 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 parotid artery ascends from the arch of 

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

 joint, where it continues as the cervical portion. 



Relations. In front, it is separated from the first piece of the sternum by the' Sternohyoid 

 and Sternothyroid muscles, the anterior portions of the left pleura and lung, the left innominate 

 vein, and the remains of the thymus gland; behind, it lies on the trachea, oesophagus, thoracic 



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



