EXTERNAL CAROTID ARTERY. 345 



the original absence of the neck in the foetus, and the comparatively late period at 

 which, when the neck is formed, the carotid artery becomes elongated with it. 



PECULIARITIES. Origin. The right carotid artery occasionally arises directly from 

 the aorta, or in conjunction with the left carotid. When it arises from the aorta, it is 

 usually the first vessel from the arch, the subclavian being displaced ; but it has been 

 found to occupy the second place, the right subclavian, or, very rarely, the left carotid 

 being the first. 



The place at which the right carotid artery commences, varies with the point of 

 bifurcation of the innominate artery. A change from the usual position on a level 

 with the upper border of the clavicle was found by R. Quain in the proportion of 

 about one case in eight and a half of those observed by him ; and it was found to 

 occur more frequently above than below that point. 



The left carotid artery varies in its origin 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 innominate 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. 



Piace of division. 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 oppo- 

 site 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, in which the carotid artery, measuring one 

 inch and a half in length, divided at the root of the neck. (" De Sedibus et Causis 

 Morbonim," &c. Epist. 29, Art. 20.) 



The common carotid artery has been found, as a very rare occurrence, to ascend in 

 the neck without dividing into its two usual terminal 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. 



Occasional branches. 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 thyroid branch ; also, in a few instances, to the vertebral artery. 



EXTERNAL CAROTID ARTERY. 



The external carotid artery, distributed mainly to the face and to the 

 walla of the cranium, is smaller than the internal carotid in young per- 

 sons ; but the two are nearly of equal size in adults. It reaches from 

 the point of division of the common carotid, opposite the upper margin of 

 the thyroid cartilage, to the neck of the condyle of the lower jaw-bone, or a 

 little lower, and there divides into its two terminal branches, the temporal 

 and the internal maxillary. It diminishes rapidly as it ascends, owing to 

 the number and size of the branches which spring from it. 



At first the external carotid lies nearer to the middle line of the body 

 than the internal carotid ; but it soon becomes superficial to that artery, at 

 the same time curving slightly forwards as it ascends to its place of division. 

 At its origin this artery is concealed by the steruo-mastoid muscle, emerging 

 from beneath which, it is covered only by the platysma myoides and the 

 fascia, and traverses the upper part of a triangular intermuscular space 

 bounded by the sterno-mastoid, omo-hyoid, and digastric muscles ; it then 

 becomes deeply placed, passing beneath the stylo-hyoid and digastric 

 muscles, and finally becoming embedded in the substance of the parotid 

 gland. In the lower part of its course it is in contact with the pharynx 



