SCO ARTERIES OF THE HEAD AND NECK. 



tion of about one case in ciglit and a half of those observed by him : and it was 

 found to occur more frequently above than below that point. 



The h-ft carotid artery varies in its orifi'iii much more frequently than the 

 right, in the greater number of its deviations from the ordinary place of origin, 

 this artery arises from, or in conjunction with the iiinominate artery ; and in 

 those cases in which the right subclavian is a separate branch of the aorta, the 

 two carotids most frequently arise by a common trunk. 



In cases of transposition, or of right aortic arch without other abnormality, 

 the left common carotid springs from a left innominate artery, which is the first 

 vessel to rise from the arch, and the right carotid is the second vessel. 



Place of dicmon. — This often deviates somewhat from its usual position; it 

 does so more frequently in an upward than in a downward direction. It is often 

 as high as the os hyoides, and occasionally much higher. It is found from time 

 to time opposite the middle of the larynx, and, in rare instances, opposite the 

 lower margin of the cricoid cartilage, or even lower. One case was observed by 

 Morgagni, m which the carotid artery, measuring one inch and a half in 

 length, divided at the root of the neck. (" De Scdibus et Causis Morbonim." 

 Epist. 29. Art. 20.) The common carotid artery has been found, as a very rare 

 occun-ence, to ascend in the neck n-lthoid diridi/i// into its two usual tenninal 

 branches ; the internal carotid artery being altogether wanting. 



In two recorded cases the common carotid artery was absent, the external and 

 internal carotids arising directly from the arch of the aorta. 



Iiclath»i to nrrvci. — In one case the pneumogastric nerve was observed to 

 descend in front of the artery. 



Oecastonal hrnnclicn. — The common carotid artery sometimes gives origin at 

 its upper part to the superior thyroid artery, and. in some rare cases, to a 

 laryngeal or an inferior thjToid branch ; also, in a few instances, to the vertebral 

 artery. 



SURGICAL ANATOMY OF THE COMMON CAROTID ARTERY. 



As the common carotid does not in ordinary cases furnish any branch, a 

 ligature can be applied to any part of the vessel except immediately at its 

 commencement and termination. It is usually tied either immediately above 

 or below the omo-hyoid muscle, the operation above the muscle being pre- 

 ferred if possible because here the artery is more superficial, and is at the same 

 tinie free from the difficulties offered by the muscles lower dowoi, and by the 

 superior thyroid veins, if the artery be secured near its bifurcation. An incision 

 three inches long is made from the level of the hyoid bone dowoiwards along the 

 inner margin of the stemo-mastoid muscle. 



Before dividing the integument it is well to ascertain whether the anterior 

 jugular vein be in the line of incision. The stemo-mastoid is slightly everted, 

 and the anterior belly of the omo-hyoid displayed, which last is then raised and 

 turned inwards. On the front of the sheath of the vessels may now be seen 

 the descendens noni nerve. The sheath is to be opened over the artery near the 

 trachea in order to avoid the internal jugular vein, and it is best to insert the 

 aneurism needle conve;yang the ligature on the outer side of the artery, for thus 

 the vein and the pneumogastric nerve will be most effectually avoided. Should 

 the internal jugular vein lie in front of the artery, as it sometimes does on 

 tlie left side, and especially at the lower part of the neck on that side, it will be 

 a source of much difficulty in completing the operation, and much caution wUl 

 be required in passing the aneurism needle with the ligature about the artery. 

 Should the operation be performed at the lower part of the neck, some fibres 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. 



EXTERNAL CAROTID ARTERY. 



FORM AND POSITION. — The external carotid artery, distributed maiuly 

 to the face and to the walls of the cranium, is smaller than the internal 

 carotid in young persons : but the two are nearly of equal size in 



