EXTERNAL CAROTID. 447 



whilst in cases of aneurism of the upper part of the carotid, that part of the vessel may be 

 selected which is below the Omo-hyoid. It occasionally happens that the carotid artery bifur- 

 cates below its usual position : if the artery be exposed at its point of bifurcation, both divisions 

 of the vessel should be tied near their origin, in preference to tying the trunk of the artery near 

 its termination ; and if, in consequence of the entire absence of the common carotid, or from its 

 early division, two arteries, the external and internal carotids, are met with, the ligature should 

 be placed on that vessel which is found on compression to be connected with the disease. 



In this operation, the direction of the vessel and the inner margin of the Sterno-mastoid are 

 the chief guides to its performance. 



To tie the Common Carotid, above the Omo-hyoid. The patient should be placed on his back 

 with the head thrown back - r an incision is to be made, three inches Jong, in the direction of the 

 anterior border of the Stern o-mastoid, from a little below the angle of the jaw to a level with 

 the cricoid cartilage ; after dividing the integument, superficial fascia, and Platysma, the deep 

 fascia must be cut through on a director, so as to avoid wounding numerous small veins that are 

 usually found beneath. The head may now be brought forwards so as to relax the parts some- 

 what, and the margins of the wound held asunder by copper spatulse. The descendens noni nerve 

 is now exposed, and must be avoided, and the sheath of the vessel having been raised by forceps, 

 is to be opened over the artery to a small extent at its inner side. The internal jugular vein may 

 now present itself alternately distended and relaxed ; this should be compressed both above and 

 below, and drawn outwards, in order to facilitate the operation. The aneurism needle is now 

 passed from the outside, care being taken to keep the needle in close contact with the artery, 

 and thus avoid the risk of injuring the jugular vein, or including the vagus nerve. Before the 

 ligature is tied, it should be ascertained that nothing but the artery is included in it. 



To tie the Common Carotid, below the Omo-hyoid. The patient should be placed in the same 

 position as above mentioned. An incision about three inches in length is to be made, parallel 

 with the inner edge of the Sterno-mastoid, commencing on a level with the cricoid cartilage. 

 The inner border of the Sterno-mastoid having been exposed, the sterno-mastoid artery and a 

 large vein, the middle thyroid, will be seen, and must be carefully avoided ; the Sterno-mastoid is 

 to be drawn outwards, and the Sterno-hyoid and thyroid muscles inwards. The deep fascia must 

 now be divided below the Omo-hyoid muscle, and the sheath having been exposed, must be 

 opened, care being taken to avoid the descendens noni, which here runs on the inner or tracheal 

 side. The jugular vein and vagus nerve being then pressed to the outer side, the needle must be 

 passed round the artery from without inwards, great care being taken to avoid the inferioi 

 thyroid artery, the recurrent laryngeal, and sympathetic nerves which lie behind it. 



Collateral Circulation. After ligature of the common carotid, the collateral circulation can 

 be perfectly established, by the free communication which exists between the carotid arteries of 

 opposite sides, both without and within the cranium and by enlargement of the branches of the 

 subclavian artery on the side corresponding to that on which the vessel has been tied, the chief 

 communication outside the skull taking place between the superior and inferior thyroid arteries, 

 and the profunda cervicis, and arteria princeps cervicis of the occipital ; the vertebral taking 

 the place of the internal carotid within the cranium. 



Sir A. Cooper had an opportunity of dissecting, thirteen years after the operation, the case in 

 which he first successfully tied the common carotid (the second case in which the operation hud 

 been performed). Gay's Hospital Reports, i. 56. The injection, however, does not seem to have 

 been a successfnl one. It showed merely that the arteries at the base of the brain (circle of 

 Willis) were much enlarged on the side of the tied artery, the basilar artery on that side having 

 been one of the chief means of restoring the circulation, and that the anastomosis between the 

 branches of the external carotid on the affected side and those of the same artery on the sound 

 side was free, so that the external carotid was pervious throughout. 



EXTERNAL CAROTID ARTERY. 



The External Carotid Artery (Fig. 274) arises opposite the upper border of 

 the thyroid cartilage, and taking a slightly curved course, ascends upwards and 

 forwards, and then inclines backwards, to the space between the neck of the 

 condyle of the lower jaw, and the external meatus, where it divides into the 

 temporal and internal maxillary arteries. It rapidly diminishes in size in its 

 course up the neck, owing to the number and large size of the branches given 

 off from it. In the child, it is somewhat smaller than the internal carotid ; but 

 in the adult, the two vessels 'are of nearly equal size. At its commencement, 

 this artery is more superficial, and placed nearer the middle line than the inter- 

 nal carotid, and is contained in the triangular space bounded by the Sterno- 

 mastoid behind, the Omo-hyoid below, and the posterior belly of the Digastric 

 and Stylo-hyoid above ; it is covered by the skin, Platysma, deep fascia, and 



