INNOMINATE; COMMON CAROTID. 367 



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 

 considerable interest for the surgeon to remember in connection with the operation of including 

 this vessel in a ligature. 



Branches. The arteria innominata occasionally supplies a thyroid branch, the 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 light side, the innominate is directed to the left 

 side of the neck, instead of the right. 



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 no instance has it been attended with success. An important fact has, however, 

 been established, viz., that the circulation in the parts supplied by the artery can be supported 

 after the operation ; a fact which cannot but encourage surgeons to have recourse to it whenever 

 the urgency of the case may require it, notwithstanding that it must be regarded as peculiarly 

 hazardous. 



The failure of the operation in those cases where it has been performed has depended on sub- 

 sequent repeated secondary hemorrhage, or on inflammation of the adjoining pleural sac and 

 lung. The main obstacles to its performance are,^is the student will perceive from his dissection 

 of this vessel, its deep situation 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 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 to be carried about the same length along the upper border of the clavicle. 

 The skin is to be dissected back, and the Platysma being exposed must be 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 must be divided 

 transversely throughout the greater part of its attachment. 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 innominata is arrived at. The left vena innominata should now be depressed, the right 

 vena innominata, 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. 



It has been seen that the failure of this operation depends either upon repeated secondary 

 hemorrhage, or inflammation of the pleural sac and lung. The importance of avoiding 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 attended to. 



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 ri<2;ht 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 thorax. It 

 will, therefore, be more convenient to describe first the course and relations of 

 that portion of the left carotid which intervenes between the arch of the aorta and 

 the left sterno-clavicular articulation (see fig. 205). 



The left carotid within the thorax passes obliquely outwards from the arch of 

 the aorta to the root of the neck. In front, it is separated from the first piece of 

 the sternum by the Sterno-hyoid and Sterno-thyroid muscles, the left innominate 

 vein, and the remains of the thymus gland ; behind, it lies on the trachea, ceso- 



