CAROTID ARTERY. 



483 



opinion they have been also called arteria 

 soporifertc. 



The carotid arteries consist of 1st, the pri- 

 mitive carotids, of which the right arises from 

 the arteria innominata, while the left comes 

 directly from the arch of the aorta ; 2d, the ex- 

 ternal carotid ; and. 3d, the internal carotid : 

 these last two vessels on each side being pro- 

 duced by the bifurcation of the primitive ca- 

 rotid. 



Both primitive carotids are of equal size 

 according to Bichat, Boyer, and Cloquet; nei- 

 ther Meckel nor Tiedemann make any remark 

 as to a difference in their size, while, according 

 lo Soemmerring, the right is one-twenty-fifth 

 larger than the left in the majority of in- 

 stances. 



The origin of the right carotid from the 

 arteria innominata is opposite the right sterno- 

 clavicular articulation. The left carotid arises 

 from the transverse portion of the arch of the 

 aorta behind the first bone of the sternum, on a 

 plane with the centre of the junction of the 

 cartilages of the first pair of ribs with that bone 

 in front, and corresponding with the superior 

 edge of the second thoracic vertebra posteriorly; 

 owing to this difference in their origins, the left 

 primitive carotid is from one inch to one inch 

 and a quarter longer than the right, and is con- 

 tained within the thorax in the commencement 

 of its course; it may therefore be divided into 

 a thoracic and a cervical portion. 



The thoracic portion of the left primitive 

 carotid, by which 1 mean that portion which 

 extends from the origin of the artery to a point 

 on a level with the sterno-clavicular articulation, 

 has the following relations : anteriorly it is 

 covered by the left vena innominata, the remains 

 of the thymus gland, some loose cellular tissue, 

 and occasionally a few lymphatic glands ; in 

 front erf these the origins of the sterno-thyroid 

 and sterno-hyoid muscles separate it from the 

 sternum ; posteriorly it rests on the oesophagus, 

 left recurrent nerve, the origin of the left sub- 

 clavian artery, the left par vagum, the thoracic 

 duct, and some loose cellular tissue, in addition 

 to which the longus colli is interposed between 

 it and the front of the spinal column ; on its 

 right side it is bounded by the trachea, and on 

 its left by the phrenic nerve and the mediasti- 

 nal portion of the left pleura, which gives a 

 loose covering to a small portion of its surface, 

 against which the internal side of the apex of 

 the left lung is applied. 



The right primitive carotid and the cervical 

 portion of the left are of equal length, and have 

 similar relations : at first, in the lower part of 

 the neck these vessels of opposite sides are only 

 separated by the breadtli of the trachea : as 

 they ascend, however, they diverge from each 

 other, and are separated by the larynx and 

 thyroid body : in their ascent they seem to pass 

 backwards, owing to the prominence of the 

 larynx forwards, but in reality they cannot re- 

 cede, as they are closely applied to the front of 

 the spinal column ; they are not contorted in 

 their course, nor do they furnish any branch 

 until they arrive as high as the superior margin 



of the larynx, where each bifurcates by dividing 

 into the external and the internal carotids. 



Relations of the trunk of the Primitive 

 Carotid. Anteriorly the primitive carotid is 

 covered by the three following layers of mus- 

 cles from the sterno-clavicular articulation to 

 the level of the cricoid cartilage; 1st, the pla- 

 tysma myoides, beneath which lies the superfi- 

 cial layer of the cervical fascia; 2d, the sternal 

 portion of the sterno-cleido-mastoid ; and 3d, 

 by the sterno-hyoid, sterno-thyroid, and the 

 omo-hyoid, which latter muscle crosses the 

 sheath of the artery, having its internal edge 

 connected with the outer edge of the sterno- 

 thyroid by a dense fascia, a part of the deep 

 layer of the cervical fascia, which is firmly con- 

 nected to the posterior margin of the clavicle 

 inferiorly : between the lower part of the sterno- 

 mastoid and the front of the artery there is an 

 interval of about an inch on the left side, and 

 something less on the right, in consequence of 

 the origin of the right carotid being so much 

 more anterior on that side ; this interval is 

 filled by cellular and adipose tissue, some large 

 veins, one or more of the sub-clavicular branches 

 of the cervical plexus, and occasionally a few 

 lymphatic glands; at the level of the cricoid 

 cartilage the sterno-mastoid passes backward, 

 and the omo-hyoid coming from beneath, it 

 passes forwards to its insertion into the os 

 hyoides. Above the crossing of these two 

 muscles the carotid has no muscular covering, 

 except the platysma, from which it is separated 

 by cellular membrane, several veins from the 

 thyroid body and larynx, and some lymphatic 

 glands ; the nervus descendens noni also lies in 

 front of the primitive carotid at its upper por- 

 tion, being found sometimes within, sometimes 

 outside, and occasionally embedded in the sub- 

 stance of the wall of its sheath ; the thyroid 

 body also generally overlaps the carotid by its 

 outer edge. 



Posteriorly the carotid is bounded by the 

 longus colli and rectus capitis anticus major, 

 which separate it from the anterior surface of 

 the spinal column; the cervical cord of the 

 sympathetic nerve and its superior and middle 

 cardiac branches are closely connected to the 

 posterior part of its sheath; the vertebral artery 

 and vein are behind it at its lower part ; and 

 higher up it crosses the inferior thyroid artery 

 at a point corresponding to that at which it is 

 covered in front by the omo-hyoideus ; some- 

 times the inferior thyroid crosses over the ca- 

 rotid : the arteria cervical is ascendens often lies 

 behind the carotid towards the upper part of 

 the neck ; moreover, the recurrent nerve on the 

 right side, in its course from behind the sub- 

 clavian artery to the side of the trachea, passes 

 behind the origin of the right carotid. From 

 the relations of the primitive carotid posteriorly, 

 it is evident that it can be most effectually 

 compressed against the front of the spinal co- 

 lumn, but to continue such pressure for any 

 length of time would obviously be followed by 

 injurious effects, from the lesion to which the 

 nerves behind the sheath of the vessel would 

 be thus subjected. 



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