388 THE INNOMINATE ARTERY. 



Other branches which have been seen arising from the arch are the internal and external 

 carotids, the internal mammary, the inferior thyroid, the thyroidea ima (r. infra), and one or 

 both bronchial arteries (frequently). 



(For more detailed information as to these and some other varieties of the great arteries 

 see Turner, " On Irregularities of the Pulmonary Artery, Arch of the Aorta," &c., Brit, and 

 For. Med. Chir. Rev., THTT, 1862 ; Allen Thomson, " Description of a Case of Right Aortic 

 Arch," Glasgow Med. Journ., 1863 ; and Henle's " Handbuch.") 



INNOMINATE ARTERY. 



The innominate or brachio-cephalic artery (14 mm.), the largest of the vessels 

 which proceed from the aorta, arises from the upper surface 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, on a level with 

 the upper margin of the clavicle, where it divides into the right subclavian and 

 common carotid arteries. The place of bifurcation would, in most cases, be reached 

 by a probe passed backwards through the interval between the sternal and clavicular 

 portions of the sterno-mastoid muscle. The length of the artery usually ranges 

 from one to two inches. 



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

 sternum and the sterno-clavicular articulation, from which it is separated by the 

 sterno-hyoid and sterno-thyroid muscles, by the remains of the thymus gland, and 

 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, the upper against 

 the pleura : on its left side is the left carotid artery below, and the trachea above ; 

 and to the right is the corresponding innominate vein. 



There are usually no branches arising from this vessel. 



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

 occasionally it measures less than one inch. 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 artery. It is sometimes found dividing 

 a considerable distance below the clavicle, and sometimes, but rather less frequently, above 

 it. Though usually destitute of branches, this vessel supplies occasionally a thyroid branch, 

 the thyroidea ima, and, in rare cases, the internal mammary artery, or a thymic branch, or a 

 bronchial artery, which descends in front of the trachea. 



The thyroidea ima is an artery which occurs in about 10 per cent, of bodies. It most 

 frequently arises from the innominate trunk, but in some instances it comes from the 

 right common carotid, or from the aorta itself. More rarely it arises from the internal 

 mammary or subclavian. It varies greatly in size in different bodies, and compensates in 

 various 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 complicate the operation 

 of tracheotomy. 



COMMON CAROTID ARTERIES (F). 

 POSITION AND EELATIONS DIFFERENCE ON THE TWO SIDES. The Common 



carotid arteries of the right and left sides are nearly alike in their course and position 

 while they are in the neck ; but they differ materially in their place of origin, and 

 consequently in their length, and position at their commencement. On the right 

 side the carotid artery commences at the root of the neck behind the upper part of 

 the sterno-clavicular articulation, at the bifurcation of the innominate artery ; but 

 on the left side the carotid arises within the thorax, from the middle part of the 

 arch of the aorta, very near the origin of the innominate artery. 



While WITHIN THE THORAX, the left carotid ascends obliquely behind and at some 

 distance from the upper piece of the sternum and the sterno-hyoid and the sterno- 



1 This number indicates the order to which the artery belongs : see p. 378. 



