THE INNOMINATE ARTERY. 481 



i he remains of the thymus gland, the origin of the left carotid artery, the left 

 inferior thyroid vein, and the trachea. 



Branches. The innominate usually gives off no branches, but occasionally a 

 small branch, the thyroidea ima, is given off from this vessel. It also sometimes 

 gives off a ihymic or bronchial branch. The Thyroidea ima ascends in front of 

 the trachea to the lower part of the thyroid body, 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 is found to arise from the right common 

 carotid or from the aorta, the subclavian, or internal mammary vessels. 



PLAN OF THE RELATIONS OF THE INNOMINATE ARTERY. 



In front. 

 Sternum. 



Sterno-hyoid and Sterno-thyroid muscles. 

 Remains of thymus gland. 



Left innominate and right inferior thyroid veins. 



Inferior cervical cardiac branch from right pneumogastric nerve, 



Right side. Left side. 



Right innominate vein. [ innominate \ Remains of thymus. 



Right pneumogastric nerve. I Artery. I L e f t p aro t,i(j 



Pleura. V Left inferior thyroid vein. 



\^___^/ Trachea. 



Behind. 

 Trachea. 



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 ligature of the innominate artery, by tying 

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

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

 all the vessels of the head completely" (Surgical Anatomy of the Head ami Neck, p. 62). 

 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 he'ad and neck ; while 

 the anastomosis between the superior intercostal 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 deep epigastric, from 

 the external iliac, would, by means of its anastomosis with the internal mammary, compensate 

 fur any deficiency in the vascularity of the wall of the chest. 



Surgical Anatomy. Although the operation of tying the innominate artery has been 

 performed by several surgeons for aneurism of the right subclavian extending inward as far as 

 the Scalenus, in only five instances, according to Mr. Jacobson, has the patient survived. 

 Mott's patient, however, on whom the operation was first performed, lived nearly four weeks, 

 and Graefe's more than two months. The chief danger of the operation appears to be the fre- 

 quency of secondary hemorrhage ; but in the present day, with the practice of aseptic surgery 

 and our greater knowledge of the use of the ligature, more favorable results may be anticipated. 

 Other causes of death after operation are pleurisy, pericarditis, and suppurative cellulitis. The 

 main obstacles to the operation are, as the student will perceive from his dissection of this 

 vessel, the deep situation of the artery behind and beneath the sternum, and the number of 

 important structures which surround it in every part. 



In order to apply a ligature to this vessel, the patient is to be placed upon his back, with the 

 thorax slightly raised, the head bent a little backward, and the shoulder on the side of the', aneu- 

 rism strongly depressed, so as to draw out the artery i'rom behind the sternum into the neck. 

 An incision three or more inches long is then made along the anterior border of the Sterno-inas- 

 toid muscle, terminating at the sternal end of the clavicle. From this point a second incision is 

 carried about the same length along the upper border of the clavicle. The skin is then dissected 

 back, and the Platysma divided on a director : the sternal end of the Sterno-mastoid is now 

 brought into view, and, a director being passed beneath it and close to its under surface, so as to 

 avoid any small vessels, it is to be divided ; iu like manner the clavicular origin is to be divided 

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