THE INNOMINATE ARTERY. 729 



THE INNOMINATE ARTERY. 



The innominate artery (a. anonyma) (Figs. 679, 690), also known as the 

 brachio-cephalic, is the first as well as the largest of the three vessels which arise 

 from the arch of the aorta. It passes directly upward to the level of the right 

 sterno-clavicular articulation, where it divides into the right common carotid and 

 the right subclavian, but gives rise to no other branches. 



Relations. — Anteriorly it is separated from the sternum and from the origins of 

 the right sterno-hyoid and sterno-thyroid muscles by the left innominate vein and 

 by some fatty tissue which contains the remains of the thymus gland. Posteriorly 

 it is in relation with the trachea and the sympathetic cardiac nerves ; on the r'iglit 

 it is in contact with the right pleura and on the left of it is the left common 

 carotid artery. 



Variations. — The variations of the innominate artery have already been discussed in 

 connection with the variations of the aortic arch, since the vessel represents the proximal 

 portion of the right arch. It shows considerable variation in length, measuring between 2.8 

 and 4.5 cm., although occasionally reaching a length of 5 or even 7 cm. Occasionally it is 

 absent, the right common carotid and the right subclavian arteries arising directly from the 

 aortic arch. 



Although the innominate artery does not, as a rule, give origin to any branches except 

 the two terminal ones, yet in about 10 per cent, of cases there arises from it a vessel which is 

 termed the arteria thyroidea ima. This takes its origin usually from near the base of the 

 innominate, upon its medial surface, and passes directly upward upon the anterior surface of the 

 trachea to terminate in branches which are distributed to the isthmus and the lower portions of 

 the lobes of the thyroid body. The presence of this thyroidea ima is frequently associated with 

 a more or less extensive reduction of the size of one or other of the inferior thyroid arteries, and, 

 indeed, these arteries may be entirely supplanted by it. It is somewhat variable in its origin, 

 for, instead of arising from the innominate, it may be given off by the aortic arch, by the right 

 common carotid, by either the right or left subclavian, or, in rare cases, by one of the branches 

 of the subclavians. 



Practical Considerations. — The line of the innominate artery is from the 

 middle of the manubrium to the right sterno-clavicular joint. Its point of bifurca- 

 tion would be crossed by a line drawn backward, just above the clavicle, through 

 the interval between the sternal and clavicular portions of the sterno-mastoid muscle. 



Aneurism of the innominate arterv, often associated with aneurism of the aortic 

 arch, causes pressure-symptoms easily explained by the chief relations of the vessel. 

 They may be summarized as follows : i. Vascular, (a) arterial, weakness or irregu- 

 larity of the right radical pulse or of the right carotid or temporal pulse from inter- 

 ruption of the direct blood-current ; (d) venous, duskiness of the face and neck, 

 especially of the right side, oedema of the eyelids, protrusion of the eyeballs, lividity 

 of the lips, from pressure on the left innominate, deep jugular, and transverse 

 veins lying between the vessel and the thoracic wall ; oedema of the right arm from 

 subclavian pressure. 2. Nervous, cough and hoarseness or aphonia from involve- 

 ment of the right recurrent laryngeal : dilatation or contraction of the pupil from 

 pressure on the sympathetic ; hiccough from irritation of the phrenic ; pain, particu- 

 larly severe on the right side of the neck and head, the same side of the chest, and 

 down the right arm from pressure on the branches of the cervical and brachial 

 ple.xuses. In addition, dyspnoea and dysphagia from compression of the trachea 

 and oesophagus, and the appearance of a swelling at and above the right sterno- 

 clavicular articulation, often obliterating the suprasternal depression, are character- 

 istic symptoms. 



In endeavoring to differentiate these aneurisms from those of the arch of the 

 aorta it may be well to remember .that the position of the innominate is above, to 

 the right, and, in a way, cervico-thoracic, while that of the arch is on a lower level, 

 is median or to the left, and is wholly thoracic. 



Ligation. — Two skin incisions, each three inches in length, are made along the 

 anterior edge of the sterno-mastoid muscle and the upper border of the inner third 

 of the clavicle, uniting at an acute angle near the right-sterno-clavicular articulation. 

 The sternal portion and the greater part of the clavicular portion of the sterno-mas- 



