THE IXXOMIXATE ARTERY. 355 



the left auricular appendage ; its two branches also furnish throughout 

 their course smaller offsets, which supply the left auricle, both ventricles, 

 and the interventricular septum. 



It has been customaiy to describe the transverse branches of the coronary- 

 arteries as anastomosing in the left atuiculo-ventricular sulcus, and the des- 

 •cending branches as anastomosing near the apex of the heart, and this description 

 was never doubted till it was found by Hyrtl, as the result of separate injection 

 •of these vessels, that the branches of one coronary artery cannot be injected with 

 material introduced into the other. (Nat. Hist. Review, 1861, p. 321.) 



Varieties. — The coronary arteries have been observed m a few instances to 

 commence by a common trunk, from which they diverged and proceeded to then- 

 usual destination. The existence of three coronary arteries is not a very rare 

 .occiuTence, the thii-d being small, and arising close l3yone of the others. Meckel, 

 in one instance, observed four, the supplementary vessels appearing like branches 

 of one of the coronary arteries transfen-ed to the aorta. 



THE INNOMINATE AETERY. 



The innominate, or brachio-cephalic artery, the largest of the vessels 

 which proceed from the arch of the aorta, arises from the commence- 

 ment of the transverse portion of the arch, before the left carotid 

 artery. From this point the vessel ascends obliquely towards the right, 

 until it arrives opposite the sterno-clavicular articulation of that side, 

 nearly on a level with the upper margin of the clavicle, where it divides 

 into the right .subclavian and the right carotid arterj^ The place of 

 bifurcation would, in most cases, be reached by a probe passed back- 

 wards through the cellular interval between the sternal and clavicular 

 portions of the sterno-mastoid muscle. The length of the innominate 

 artery is very variable, but usually ranges from an inch and a half to 

 two inches. 



This artery, lying for the most part within the thorax, is placed 

 behind the first bone of the sternum, from which it is separated by the 

 :sterno-hyoid and sterno- thyroid muscles, and a little lower down by the 

 •left innominate vein, which crosses the artery at its root. The lower 

 part of the innominate artery lies in front of the trachea, which it 

 vcrosses obliquely : on its left side is the left carotid artery, with the 

 thymus gland or its remains ; and to t!ie right is the corresponding 

 brachio-cephalic vein and the pleura. 



No branches usually arise from this vessel. 



Varieties. — The length of the innominate artery sometimes exceeds two inches, 

 and occasionally it measures only one inch or less. Its place of division is a 

 point of surgical interest, inasmuch as upon it in a great measure depends the 

 accessibility of the innominate in the neck, and the length of the right subclavian 

 arterj-. It has sometimes been found dividing at a considerable distance above 

 the clavicle, and sometimes, but less frequently, below it. Though usually des- 

 titute of branches, this vessel has been observed to supply a thyroid branch, the 

 thyroidea ima, and sometimes a thymic branch, or a bronchial, which descends in 

 front of the trachea. 



The thi/roidea ima is an occasional artery. When present, it usually arises (as 

 already stated) from the innominate trunk, but in some instances it has been observed 

 to come from the right common carotid artery, or from the aorta itself. More 

 rarely it arises from the right internal mammary, or the right subclavian. It ia 

 of very different size in different bodies, and compensates in varioiis degrees for 

 deficiencies or absence of the other thyroid arteries. It ascends to its destination 

 in front of the trachea, and its presence might therefore complica.te the operation 

 of tracheotomy, 



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