CAROTID ARTERY. 483 



opinion they have been also called arterial of the larynx, where each bifurcates by dividing 



soporifera. into the external and the internal carotids, 



The carotid arteries consist of 1st, the pri- Relations of the trunk of the Primitive 



mitive carotids, of which the right arises from Carotid. Anteriorly the primitive carotid is 



the arteria innominata, while the left comes covered by the three following layers of mus- 



directly from the arch of the aorta ; 2d, the ex- cles from the sterno-clavicular articulation to 



ternal carotid ; and, 3d, the internal carotid: the level of the cricoid cartilage; 1st, the pla- 



these last two vessels on each side being pro- tysma myoides, beneath which lies the superfi- 



duced by the bifurcation of the primitive ca- cial layer of the cervical fascia; 2d, the sternal 



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



Both primitive carotids are of equal size by the sterno-hyoid, sterno-thyroid, and the 

 according to Bichat, Boyer, and Cloquet ; nei- omo-hyoid, which latter muscle crosses the 

 ther Meek el nor Tiedemann make any remark sheath of the artery, having its internal edge 

 as to a difference in their size, while, according connected with the outer edge of the sterno- 

 to Soemmerring, the right is one-twenty-fifth thyroid by a dense fascia, a part of the deep 

 larger than the left in the majority of in- layer of the cervical fascia, which is firmly con- 

 stances, nected to the posterior margin of the clavicle 



The origin of the right carotid from the inferiorly: between the lower part of the sterno- 



arteria innominata is opposite the right sterno- mastoid and the front of the artery there is an 



clavicular articulation. The left carotid arises interval of about an inch on the left side, and 



from the transverse portion of the arch of the something less on the right, in consequence of 



aorta behind the first bone of the sternum, on a the origin of the right carotid being so much 



plane with the centre of the junction of the more anterior on that side; this interval is 



cartilages of the first pair of ribs with that bone filled by cellular and adipose tissue, some large 



in front, and corresponding with the superior veins, one or more of the sub-clavicular branches 



edge of the second thoracic vertebra posteriorly ; of the cervical plexus, and occasionally a few 



owing to this difference in their origins, the left lymphatic glands ; at the level of the cricoid 



primitive carotid is from one inch to one inch cartilage the sterno-mastoid passes backward, 



and a quarter longer than the right, and is con- and the omo-hyoid coming from beneath, it 



tained within the thorax in the commencement passes forwards to its insertion into the os 



of its course; it may therefore be divided into hyoides. Above the crossing of these two 



a thoracic and a cervical portion. muscles the carotid has no muscular covering, 



The thoracic portion of the left primitive except the platysma, from which it is separated 



carotid, by which I mean that portion which by cellular membrane, several veins from the 



extends from the origin of the artery to a point thyroid body and larynx, and some lymphatic 



on a level with the sterno-clavicular articulation, glands ; the nervus descendens noni also lies in 



has the following relations : anteriorly it is front of the primitive carotid at its upper por- 



covered by the left vena innominata, the remains tion, being found sometimes within, sometimes 



of the thymus gland, some loose cellular tissue, outside, and occasionally embedded in the sub- 



and occasionally a few lymphatic glands; in stance of the wall of its sheath; the thyroid 



front of these the origins of the sterno-thyroid body also generally overlaps the carotid by its 



and sterno-hyoid muscles separate it from the out er edge. 



sternum ; posteriorly it rests on the oesophagus, Posteriorly the carotid is bounded by the 



left recurrent nerve, the origin of the left sub- longus colli and rectus capitis anticus major, 



clavian artery, the left par vagum, the thoracic which separate it from the anterior surface of 



duct, and some loose cellular tissue, in addition the spinal column; the cervical cord of the 



to which the longus colli is interposed between sympathetic nerve and its superior and middle 



it and the front of the spinal column ; on its cardiac branches are closely connected to the 



right side it is bounded by the trachea, and on posterior part of its sheath; the vertebral artery 



its left by the phrenic nerve and the mediasti- and vein are behind it at its lower part ; and 



nal portion of the left pleura, which gives a higher up it crosses the inferior thyroid artery 



loose covering to a small portion of its surface, at a point corresponding to that at which it is 



against which the internal side of the apex of covered in front by the omo-hyoideus ; some- 



the left lung is applied. times the inferior thyroid crosses over the ca- 



The right primitive carotid and the cervical rotid : the arteria cervical is ascendens often lies 

 portion of the left are of equal length, and have behind the carotid towards the upper part of 

 similar relations : at first, in the lower part of the neck ; moreover, the recurrent nerve on the 

 the neck these vessels of opposite sides are only right side, in its course from behind the sub- 

 separated by the breadth of the trachea : as clavian artery to the side of the trachea, passes 

 they ascend, however, they diverge from each behind the origin of the right carotid. From 

 other, and are separated by the larynx and the relations of the primitive carotid posteriorly, 

 thyroid body : in their ascent they seem to pass it is evident that it can be most effectually 

 backwards, owing to the prominence of the compressed against the front of the spinal co- 

 larynx forwards, but in reality they cannot re- lumn, but to continue such pressure for any 

 cede, as they are closely applied to the front of length of time would obviously be followed by 

 the spinal column ; they are not contorted in injurious effects, from the lesion to which the 

 their course, nor do they furnish any branch nerves behind the sheath of the vessel would 

 until they arrive as high as the superior margin be thus subjected. 



& I At 



