SUBCLAVIAN ARTERIES. 



819 



the altered direction of the nerve : " In the ear- 

 lier periods of the existence of the foetus, the 

 rudiment of the head appears as a small pro- 

 jection from the upper and anterior part of 

 the trunk, the neck not being yet developed. 

 The larynx at this time is placed behind the 

 ascending portion of the arch of the aorta ; 

 while the brain, as it then exists, is situated so 

 low, as to rest on the thymus gland and front 

 of that vessel. Hence it is that the inferior 

 laryngeal nerves pass back to the larynx, se- 

 parated by the ascending aorta, the left going 

 through its arch, while the right goes below 

 the arteria innominata. 



" As gestation advances, the head becomes 

 more distinct, and the neck begins to be 

 formed after the second month, which, as it 

 lengthens, has the effect of removing the 

 brain upwards to a greater distance, and of 

 drawing out the larynx from the chest, in 

 consequence of which the nerves of the par 

 vagum and their recurrents become elongated, 

 and hence the circuitous route the latter are 

 found to take afterwards, forming loops in 

 which the aorta and right subclavian artery 

 are, as it were, suspended."* 



2. The left subclavian artery is much less 

 liable to vary in the mode of its origin than 

 the right ; the varieties observed are also 

 fewer in number, a. The origin of the left sub- 

 clavian artery is sometimes more approximated 

 than usual to the origin of the left carotid, and 

 in a few instances, b. its origin is fused into 

 that of the latter, so that these two vessels 

 arise by a common trunk, which is a left 

 arteria innominata, 



It has been observed in those instances 

 where the arch of the aorta is reversed, so as 

 to pass from left to right, that the same irre- 

 gularities affect the transposed branches which 

 then arise from it, as have been stated to 

 occur when the arch holds its more usual po- 

 sition. 



Branches of the subclavian arteries. In the 

 number and arrangement of the branches of 

 the subclavian artery so much variety occurs, 

 that no general description could, perhaps, be 

 given, which would accurately describe their 

 arrangement in any one instance, and hence, 

 in works on anatomy, much discrepancy exists 

 on this subject; the following description 

 agrees with that of the best authorities in 

 this country, and is strictly in accordance 

 with the accurate statistical details of Professor 

 Quain. 



In its first stage the subclavian artery usually 

 gives origin to the following branches the 

 vertebral, internal mammary, and thyroid axis ; 

 the last, after a very short course, divides 

 in a radiating manner into the inferior thyroid, 

 the supra-scapular (transversalis humerij, and 

 the transverse cervical (transversalis colli) 

 arteries ; besides, in the majority of instances, 

 the left subclavian artery, in its first stage, 

 furnishes (in addition to the branches already 



* Dr. Hart, in Edinb. Mod. and Surg. Journal, 

 1826. 



enumerated) the superior intercostal artery, a 

 branch which, on the right side, more fre- 

 quently arises under cover of the scalenus 

 anticus muscle. All these branches arise 

 nearer to the scaleni muscles, and are conse- 

 quently more immediately covered by the 

 internal jugular vein on the left side of the 

 neck than on the right. 



The position of these branches of the .sub- 

 clavian artery, especially on the right side, 

 is of much interest in a surgical point of view. 

 " The situation in which the branches arise 

 from any large artery is an important con- 

 sideration in its history, because of the influ- 

 ence which their presence has on the result 

 of an operation for the cure of aneurism. 

 And, considering the shortness of the trunk, 

 the size of the offsets, and the manner of 

 their arrangement on the parent vessel, it may 

 be confidently stated that there is no artery 

 in which the influence alluded to is more 

 considerable than in the subclavian."* 



The following statistics, derived from the 

 author just quoted, are useful to show the 

 average length of the subclavian artery, from 

 its origin to the point where its first branch 

 arises; in other words, the extent of the 

 artery in its first stage, suitable for the appli- 

 cation of a ligature. 



In sixty-five bodies examined, this distance 

 measured 



A inch and under - - - in 8 



More than inch and not exceed- 

 ing 1 inch - - - - 33 



More than 1 inch and not exceed- 

 ing 1J inch - - 23 



If inch (the extreme length) - 1 



Occasionally, the vertebral, or inferior thy- 

 roid artery, has been seen to arise very close 

 to the arteria innominata. 



In the second stage the subclavian artery 

 most frequently gives off but a single branch, 

 which soon subdivides into the cervicalis pro- 

 funda and superior intercostal arteries. It is 

 less usual for these two arteries to arise 

 separately; thus, in 285 examinations, this 

 occurred in the proportion of but 1 to 20A, 

 whereas the former arrangement existed in 

 266 out of the entire number. 



In the majority of instances no branches 

 arise from the subclavian artery external to the 

 scaleni; but the posterior scapular artery (in 

 general the continued trunk of the transver- 

 salis colli) frequently arises from the third 

 stage of the subclavian, and so frequently, 

 indeed, that Cruveilhier regards it, not as a 

 variety, but as the normal arrangement. It 

 is computed by Professor Quain that this 

 occurs in the proportion of 1 in 2 cases. 



I. Vertebral artery. This artery, which is 

 the first and largest, is at the same time one 

 of the most regular of the branches of the 

 subclavian artery, from the upper and posterior 



* Anatomy of the Arteries of the Human P.ody, 

 with its Applications to Pathology and Operative 

 Surgery (Plates). By Prof. Quain. Part VI. 



3 G 2 



