The leading facts in the foregoing account of the common carotid artery will here be brought together in connection with the performance of an operation for tying the artery, as in a case of aneurism. — As this artery does not, save in very rare instances, furnish any branch, (in a practical or surgical point of view the branches sometimes found to arise close to its upper end may be disregarded,) a ligature can be applied to any part of the vessel except immediately at its commencement or termination.
When the case is such as to allow a choice, the point which probably combines most favorable circumstances for the operation, is opposite the lower end of the larynx. Here a large space would, in ordinary cases, intervene between the ligature and the ends of the vessel ; and at the same time this part is free from the difficulties offered by the muscles lower down, and by the superior thyroid veins, if the artery be secured near its bifurcation. But it has been shown above that the carotid artery occasionally bifurcates below the usual position — opposite the lower margin of the larynx, and even, however rarely, lower than this. In such cases, should the artery be laid bare at the point of division, it would be best to tie the two parts separately, close to their origin, in preference to tying the common trunk near its end. If, in consequence of very early division of the common carotid or its entire absence (cases which, however, are of extremely rare occurrence) two arteries (the external and in- ternal carotids) should happen to come into view in the operation supposed, the most judicious course would doubtless be to place the ligature on that artery which, upon trial, as by pressure, should prove to be connected with the disease.
In performing the operation, the direction of the vessel and the inner margin of the sterno-mastoid muscle are the surgeon's guides for the line of incision. Before dividing the integument it is well to ascertain whether the anterior jugular vein be in the line of incision. Should the operation be performed at the lower part of the neck, some fibers of the muscles will require to be cut across in order to lay the artery bare with facility ; and the necessity for this step increases in approaching towards the clavicle. After the superficial structures have been divided, assistance will be derived from the trachea or the larynx, as well as from the pulsation, in determining the exact situation of the artery. The trachea, from its roughness, may be readily felt in the wound, even while the parts covering it have still some thickness. The sheath of the vessels is to be opened over the artery — near the trachea — for thus the jugular vein is most easily avoided. Should the vein lie in front of the artery, as it sometimes does on the left side, and especially at the lower part of the neck on that side, the vein in question will be a source of much difficulty in completing the operation, i. e. in passing the aneurism needle with the ligature about the artery. I have had occasion to observe the embarrassment arising from this cause in the living body in an ope- ration on the left carotid artery. To surmount the difficulty much caution is required. The operator will find it advantageous to have the circulation in the vein (which in such operation becomes turgid and very large) arrested at the upper end of the wound by means of an assistant's finger. In most cases, if not in all, it is best to insert the aneurism needle conveying the ligature, on the outer side of the artery, for thus the vagus nerve and the jugular vein will be most effectually avoided.