BRANCHES FROM THE ARCH OF THE AORTA. 197 



Innominata, the Left Primitive Carotid, and the Left Subcla- 

 vian. 



The Arteria Innominata is first in its origin : in ascending 

 from left to right in front of the trachea, and behind the trans- 

 verse vein, it crosses the trachea very obliquely ; is from an inch 

 to an inch and a half, and sometimes, though rarely, two inches 

 long, when it divides into the right subclavian and the right pri- 

 mitive carotid. The left primitive carotid arises from the aorta, 

 close upon the left border of the innominata ; frequently, indeed, 

 from a part of it. The left subclavian, though at its origin 

 near the left carotid, generally leaves a distinct interval of one, 

 two, or three lines. The relative situation of these trunks is 

 particularly alluded to in the account of the superior mediasti- 

 num. The two last are, of course, longer than the correspond- 

 ing trunks of the right side, by the whole length of the arteria 

 innominata. With the exceptions connected with their mode of 

 origin, the arterial trunks of the two sides are exactly alike, 

 and have the same mode of distribution. 



The Common Carotid Artery (Carolis Pritnitiva) being a 

 branch of the innominata on the right side, and of the aorta on 

 the left, goes up the neck to terminate just below the cornu of 

 the os hyoides. In the early part of its course, the right one is 

 more inclined outwardly than the left, owing to its origin from 

 the arteria innominata in front of, and to the right side of the 

 trachea ; whereas, the left ascends almost vertically. 



At the lower part of the neck, just above the sternum and 

 the clavicle, the carotid is covered by the sterno-hyoid and thy- 

 roid muscles, and by the sternal pontion of the sterno-cleido- 

 mastoid. It is crossed obliquely on a line with the lower part 

 of the thyroid cartilage of the larynx, by the omo-hyoid muscle. 

 It lies at the side of the thyroid gland, the trachea, the larynx, 

 the oesophagus, and pharynx, in front of the transverse processes 

 of the cervical vertebrae, and the longus colli muscle; having 

 on its outer margin, but somewhat in front, the internal jugu- 

 lar vein, and the pneumogastric ner.ve enclosed in the same 

 sheath, and the sympathetic nerve behind. At the side of the 

 larynx, the caroted is very superficial, and, with the exception 

 of being crossed by the omo-hyoideus muscle, it is only covered 

 by the plalysma myodes and the integuments. 



18* 



