268 COMMON CAROTID ARTERIES. 



and ascends obliquely to the right sterno-clavicular articulation, 

 where it divides into the right carotid and right subclavian artery. 



Relations. It is in relation, in front with the left vena innomi- 

 nata, the thymus gland, and the origins of the sterno-thyroid and 

 sterno-hyoid muscles, which separates it from the sternum. Behind 

 with the trachea, pneumogastric nerve and cardiac -nerves; exter- 

 nally with the right vena innominata and pleura; and internally with 

 the origin of the left carotid. 



Plan of the relations of the Arteria Innominata. 



In Front. 



Left vena innominata, 

 Thymus gland, 

 Sterno-thyroid, 

 Sterno-hyoid. 



Right Side. 



Right vena innominata, 

 Pleura. 



Arteria innominata. 



Left Side. 

 Left carotid. 



Behind. 

 Trachea, 



Pneumogastric nerve, 

 Cardiac nerves. 



The arteria innominata occasionally gives off a small branch 

 which ascends along the middle of the trachea to the thyroid gland. 

 This branch was described -by Neubauer,. and Dr. Harrison names 

 it the middle thyroid artery. A knowledge of its existence is ex- 

 tremely important in performing the operation of tracheotomy. 



COMMON CAROTID ARTERIES. 



The common carotid arteries (xapa, the head) arise, theright from 

 the bifurcation of the arteria innominata opposite the right sterno- 

 clavicular articulation, the left from the arch of the aorta. It fol- 

 lows, therefore, that the right carotid is shorter than the left; it is 

 also more anterior; and, in consequence of proceeding from a branch 

 instead of from the main trunk, it is larger than its fellow. 



The Rig/it common carotid artery (fig. 102, No. 5) ascends the 

 neck perpendicularly, from the right sterno-clavicular articulation 

 to a level with the upper border of the thyroid cartilage, where it 

 divides into the external and internal carotid. 



The Left common carotid (fig. 102, No. 11) passes somewhat ob- 

 liquely qutwards from the arch of the aorta to the side of the neck, 

 and thence upwards to a level with the upper border of the thyroid 

 cartilage, where it divides like the right common carotid into the 

 external and internal carotid. 



Relations. The right common carotid rests, first, upon the longus 

 colli muscle, then upon the rectus anticus major, the sympathetic 

 nerve being interposed. The inferior thyroid artery and recurrent 

 laryngeal nerve pass behind it at its lower part. To its inner side 

 is the trachea, recurrent laryngeal nerve, and larynx; to its outer 

 side, and enclosed in the same sheath, the jugular vein and pneumo- 



