484 



CAROTID ARTERY. 



Externally the carotid artery is bounded by 

 the internal jugular vein and the pneumo-gas- 

 tric nerve, both of which are contained within 

 its sheath ; the vein when distended advances 

 in front of it and partly conceals it ; the nerve 

 lies in the posterior part of the sheath, behind 

 and between the artery and vein, more closely 

 attached to the latter vessel ; on the left side 

 the internal jugular vein lies closer to the ca- 

 rotid, in front of which it passes at the lower 

 part of the neck in its course to the vena inno- 

 minata; on the right side the jugular vein is 

 separated from the carotid infenorly by a small 

 intervening space, principally occupied by cel- 

 lular tissue, in consequence of the vein of this 

 side descending to join the commencement of 

 the superior cava in a perpendicular course 

 further from the mesial line than the point at 

 which the carotid is given off from the arteria 

 innominata. 



Internally the carotid is bounded by the 

 trachea at its lower part; higher up by the 

 thyroid body and the inferior constrictor of the 

 pharynx, by which it is separated from the 

 cncoid and thyroid cartilages ; the recurrent 

 nerve also lies on its inner side, but separated 

 from it by a quantity of loose cellular tissue; 

 in addition to the foregoing relations, the left 

 carotid lies in contact with the oesophagus. 



The varieties to which the origins of the 

 carotid arteries are subject are the following : 

 1 . the right carotid sometimes arises separately 

 from the aorta ; this variety occurs when there 

 are four large trunks arising from the arch of 

 the aorta, of which the right carotid is the first, 

 and the right subclavian the last in order ; 2. 

 sometimes the arteria innominata gives origin 

 to the left carotid, in addition to the right ca- 

 rotid and right subclavian, in which case the 

 left carotid has to cross in front of the lower 

 part of the trachea to enter upon its cervical 

 course ; 3. the right and left carotids some- 

 times spring from a common trunk, which 

 arises from the arch of the aorta between the 

 right and left subclavian arteries ; in this variety 

 as well as in the preceding, the situation of the 

 carotids in front of the trachea exposes them to 

 the danger of being wounded in the operation 

 of tracheotomy, in performing winch the sur- 

 geon should always be prepared to meet with 

 the existence of such irregularities of distribu- 

 tion: 4. the left carotid sometimes arises from 

 a left arteria innominata, which also gives oft" 

 the left subclavian. (See AORTA.) 



The bifurcation of the primitive carotid most 

 frequently occurs opposite the superior margin 

 of the thyroid cartilage, in front of the third 

 cervical vertebra; it may, however, take place 

 above or below that point. It sometimes bifur- 

 cates opposite the cornu of the os hyoides, or, 

 which rarely happens, behind the angle of the 

 lower jaw ; in cases where the bifurcation is 

 higher than usual, the primitive carotid often 

 furnishes some of the branches ordinarily 

 arising from the external carotid. The high 

 bifurcation is an approximation to that condi- 

 tion of the carotid in which no bifurcation 

 takes place, but where the primitive carotid, 



after having given all the branches which the 

 external carotid usually supplies, enters the 

 cranium and becomes the internal carotid. 

 2. The primitive carotid sometimes bifurcates 

 lower down in the neck than usual. I have 

 seen such a. bifurcation occurring on both sides 

 in an old female subject, as low as the inferior 

 border of the thyroid body. 



The bifurcation of the carotid has the same 

 relation to the larynx at all periods of life : it 

 is more distant from the angle of the jaw in 

 the infant than in the adult ; the depth of the 

 lower jaw in the former being much less, owing 

 to the non-development of the roots of the 

 teeth and alveolar processes : in old persons 

 who have lost their teeth, and whose alveolar 

 processes have been absorbed, the jaw being 

 in the edentulous condition, the angle of the 

 jaw is carried forward and thus removed farther 

 from the bifurcation of the carotid. By de- 

 pressing the head the angle of the jaw is 

 brought nearer to the bifurcation ; while the 

 distance between these parts may be consi- 

 derably increased by throwing the head back- 

 wards. 



The bifurcation of the primitive carotid gives 

 origin to the external and internal carotids ; 

 the former of these supplies the larynx, thyroid 

 body, pharynx, throat, face, and external parts 

 of the head; the latter is distributed to the 

 brain and the internal parts of the organs of 

 hearing and vision. These two vessels lie close 

 together at their origins. The internal is at 

 first more superficial and more external in 

 situation than the external, but becomes the 

 more deeply situated of the two as they ascend. 

 They are nearly of equal size in the adult when 

 the bifurcation occurs at the usual place; while 

 in the infant the internal is larger than the 

 external. 



THE EXTERNAL CAROTID, (urttrio, carotis 

 externa, superficialis vel anterior, Samm. j'a- 

 ciale of Chuussier,) extends from the bifurca- 

 tion of the primitive carotid to the neck of the 

 condyle of the lower jaw, where it terminates 

 by dividing into the superficial temporal and 

 internal maxillary arteries. In this course it 

 describes a curve, the concavity of which is 

 outwards and a little backwards, as it ascends 

 between the ear and the ramus of the lower 

 jaw. At first it is superficial, merely covered 

 by the integuments, platysma and cervical 

 fascia; it then ascends under the ninth or 

 hypoglossal nerve and the posterior belly of the 

 digastric and stylo-hyoid muscles, and buries 

 itself in the substance of the parotid gland. In- 

 ternally it rests at first on the commencement of 

 the internal carotid, then over the middle con- 

 strictor of the pharynx, the stylo-pharyngeus 

 and stylo-glossus muscles, the glosso-pharyn- 

 geal nerve and the styloid process of the tem- 

 poral bone; the superior and inferior pharyn- 

 geal nerves coming from the par vagum also 

 pass under it in their course to the pharyngeal 

 plexus. The part of the parotid gland which 

 the external carotid first enters is the internal 

 surface of its lower extremity, consequently 

 the whole thickness of the gland covers it at 



