EXTERNAL CAROTID 371 



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 ; an incision is to be made, three inches long, in the direction of the 

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

 the cricoid cartilage : after dividing the integument, superficial fascia, and Flatysma, 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 must be held asunder by copper spatulae. 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. The internal jugular vein will 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 those contact with ti.e artery, and thus 

 avoid the risk of injuring the jugular vein, or including the vagus nerve. Be/ore the ligature is 

 secured, 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 

 situation 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 Sterne-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 inferior 

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



Collateral Circulation. After ligation 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. 



EXTERNAL CAROTID ARTERY. 



The external carotid artery (fig. 207) arises opposite the upper border of the 

 thyroid cartilage, and, taking a slightly curved course, ascends upwards and for- 

 wards, and then inclines backwards, to the space between the neck of the coudyle 

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

 and internal maxillary arteries. It rapidly diminishes in size as it ascends 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 internal carotid, and is con- 

 tained 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 anterior margin of the Sterno- 

 mastoid, crossed by the hypoglossal nerve, and by the lingual and facial veins ; 

 it is afterwards crossed by the Digastric and Stylo-hyoid muscles, and higher 

 up passes deeply into the substance of the parotid gland, where it lies be- 

 neath the facial nerve, and the junction of the temporal and internal maxillary 

 veins. 



Internally are the hyoid bone, the wall of the pharynx, and the ramus of the 

 jaw, from which it is separated by a portion of the parotid gland. 



Behind it, near its origin, is the superior laryngeal nerve ; and, higher up, it is 

 separated from the internal carotid by the Stylo-glossus and Stylo-pharyngeus 

 muscles, the glosso-pharyngeal nerve, and part of the parotid gland. 



