THE COMMOX CAROTID ARTERIES. 549 



its middle, and the anterior jugular vein below. Behind, the artery lies in front 

 of the cervical portion of the spine, resting first on the Longus colli muscle, then 

 on the Rectus capitis auticus major, from which it is separated by the sympathetic 

 nerve. The recurrent laryngeal nerve and inferior thyroid artery cross behind the 

 1 at its lower part. Internally, it is in relation with the trachea and thyroid 

 gland, the inferior thyroid artery and recurrent laryngeal nerve being interposed : 

 higher up. with the larynx and pharynx. On its outer side are placed the internal 

 jugular vein and pneumogastric nerve 



At the lower part of the neck the internal jugular vein on the right side 

 diverges from the artery, but on the left side it approaches it. and often cr<:- - 

 its lower part. This is an important fact to bear in mind during the performance 

 of any operation on the lower part of the left common carotid artery. 



PLAN OF THE RELATIONS OF THE COMMON CAROTID ARTERY. 



Externally. 



Integument, and superficial fascia. 

 Deep cervical fascia. 

 Platysma. 



Sterno-mastoid. Internally. 



Sterno-hyoid. /^^ ^X Trachea. 



Sterno-thyroid. / Thyroid gland. 



Oruo-hyoid. Common Recurrent laryngeal nerve. 



Descendens and Couimunicans by- Inferior thyroid artery. 



poglossi nerves. Larynx. 



Sterno-mastoid artery. Pharynx. 



Superior and middle thyroid veins. 

 Anterior jugular vein. 

 Internal jugular vein. 

 Pneumogastric nerve. 



Behind. 



Longus colli. Sympathetic nerve. 



Rectus capitis anticus major. Inferior thyroid artery. 



Recurrent laryngeai nerve. 



Peculiarities as to Origin. The right common carotid may arise above or below its usual 

 point, the upper border of the sterno-clavicular articulation. This variation occurs in one out of 

 about eiirht cases and a halt', and the origin is more frequently above than below the usual point ; 

 or the artery may arise as a separate branch from the arch of the aorta or in conjunction with the 

 left carotid. The hit common carotid varies more frequently in its origin than the right. In 

 the majority of abnormal cases it arises with the innominate artery, or. if the innominate artery 

 is absent, the two carotids arise usually by a single trunk. The left carotid is occasionally the 

 first branch given off from the arch of the aorta. It rarely joins with the left subclavian, except 

 in cases of transposition of the arch. 



Peculiarities as to Point of Division. The most important peculiarities of this vessel, 

 in a surgical point of view, relate to its place of division in the neck. In the majority of 

 abnormal cases this occurs higher than usual, the artery dividing into two branches opposite 

 the hyoid bone, or even higher; more rarely, it occurs below its usual place, opposite the 

 middle of the larynx or the lower border of the cricoid cartilage ; and one case is related by 

 Morgairni where the common carotid, only an inch and a half in length, divided at the root of 

 the neck. Very rarely the common carotid ascends in the neck without any subdivision, the 

 internal carotid being wanting: and in a few cases the common carotid has been found to be 

 absent, the external and internal carotids arising directly from the arch of the aorta. This 

 peculiarity existed on both sides in some instances, on one side in others. 



Occasional Branches. The common carotid usually gives off no branch previous to its 

 bifurcation : but it occasionally gives origin to tbe superior thyroid or its laryngeal branch, the 

 inferior thyroid, or. more rarely, the vertebral artery. 



Surface Marking. The carotid arteries are overlapped throughout their entire extent by 

 tbe anterior border of the Sterno-mastoid muscle, but their course does not correspond to the 

 border of tbe muscle, which passes in a somewhat curved direction from the mastoid process to 

 the sterno-clavicular joint. The course of the artery is indicated more exactly by a line drawn 

 from tbe sternal end of the clavicle below, to a point midway between the angle of the jaw and 

 tbe mastoid process above. That portion of the line below the Wei of the upper border of the 

 thyroid cartilage would represent the course of tbe vessel. 



Surgical Anatomy. The operation of tying the common carotid artery may be necessary 

 in a case of wound of that vessel or its branches, in aneurism, or in a case of pulsating tumor of 

 tbe orbit or skull. If the wound involves tbe trunk of the common carotid, it will be necessary 

 to tie the artery above and below the wounded part. But in cases of aneurism, or where one of 



