INNOMINATE; COMMON CAROTID. 443 



the clavicle ; less frequently it divides below it. la the former class of cases, its length may ex- 

 ceed two inches ; and, in the latter, be reduced to an inch or less. These are points of consider- 

 able interest for the surgeon to remember in connection with the operation of tying this vessel. 



Branches. The arteria innominata occasionally supplies a thyroid branch (middle thyroid 

 artery), which ascends along the front of the trachea to the thyroid gland ; and sometimes, a 

 thymic or bronchial branch. The left carotid is frequently joined with the innominate artery at 

 its origin. Sometimes, there is no innominate artery, the right subclavian arising directly from 

 the arch of the aorta. 



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, passed 

 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 and Neck, page 62.) The 

 branches by which this circulation would be carried on are very numerous ; thus, all the com- 

 munications 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 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 lower 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 epigastric, 

 from the external iliac, would by means of its anastomosis with the internal mammary, compen- 

 sate for any deficiency in the vascularity of the wall of the chest. 



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

 formed by several surgeons, for aneurism of the right subclavian extending inwards as far as the 

 Scalenus, in only one instance has it been attended with success. 1 Mott's patient, however, on 

 whom the operation was first performed, lived nearly four weeks, and Graefe's more than two 

 months. The main obstacles to the operation are, as the student will perceive from his dissec- 

 tion 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 

 shoulders raised, and the head bent a little backwards, so as to draw out the artery from behind 

 the sternum into the neck. An incision two inches long is then made along the anterior border 

 of the Sterno-mastoid 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, the muscle is to be divided transversely through- 

 out the greater part of its attachment. By pressing aside any loose cellular tissue or vessels 

 that may now appear, the Sterno-hyoid and Sterno-thyroid muscles will be exposed, and must be 

 divided, a director being previously passed beneath them. The inferior thyroid veins now come 

 into view, and must be carefully drawn either upwards or downwards, by means of a blunt hook. 

 On no account should these vessels be divided, as it would add much to the difficulty of the 

 operation, and endanger its ultimate success. After tearing through a strong fibro-cellular 

 lamina, the right carotid is brought into view, and being traced downwards, the arteria innomi- 

 nata is arrived at. The left vena innominata should now be depressed, the right vena innomi- 

 nata, the internal jugular vein, and pneumogastric nerve drawn to the right side ; and a curved 

 aneurism needle may then be passed around the vessel, close to its surface, and in a direction 

 from below upwards and inwards ; care being taken to avoid the right pleural sac, the trachea, 

 and cardiac nerves. ^The ligature should be applied to the artery as high as. possible, in order to 

 allow room between it and the aorta for the formation of a coagulum. The importance of avoid- 

 ing the thyroid plexus of veins during the primary steps of the operation, and the pleural sac 

 whilst including the vessel in the ligature, should be most carefully borne in mind, since secondary 

 hemorrhage or pleurisy have been the cause of death in all the cases hitherto operated on. 



COMMON CAROTID ARTERIES. 



The Common Carotid Arteries, although occupying a nearly similar position 

 in^the neck, differ in position, and, consequently, in their relations at their 

 origin. The right carotid arises from the arteria innominata, behind the right 

 sterno-clavicular articulation ; the left from the highest part of the arch of the 

 aorta. The left carotid is, consequently, longer and placed more deeply in the 



1 The operation was performed by Dr. Smyth, of New Orleans : see the New Sydenham So- 

 ciety's "Biennial Retrospect," for 1865-1866, page 346. 



