SUBCLAVIAN ARTERIES. 



817 



connected with the artery of the left side, 

 exclusively. The former holds a double relation 

 to that vessel ; in the thorax it passes behind it, 

 in the neck it rises high above it, and then 

 bends downwards in front of it, to oprn into 

 the confluence of the great veins. The oeso- 

 phagus, as has been mentioned, lies to the 

 right of the artery. 



The differences which have thus been 

 pointed out, are of material importance with 

 reference to the operations upon these two 

 arteries. 



In the remainder of their course the sub- 

 clavian arteries are perfectly symmetrical, 

 and one and the same description will apply 

 to both. 



Subclaman arteries in their second stage. 

 In its second stage each subclavian artery lies 

 in a remarkable intermuscular space, bounded 

 by the scaleni muscles. These muscles (sca- 

 lenus anticus and scalenus posticus) are closely 

 approximated to each other at their attach- 

 ment to the tubercles of the cervical trans- 

 verse processes ; but in descending to their 

 insertions they diverge, leaving between them 

 a space truly triangular, of which the base, 

 placed inferiorly, corresponds to the first rib, 

 and to a small portion of the second. In 

 this space the subclavian artery, the brachial 

 plexus of nerves, and the cone of the pleura, 

 are situated. In front, the artery is in contact 

 with the anterior wall of this triangle, consti- 

 tuted by the scalenus anticus muscle ; behind, 

 it is separated from the posterior boundary of 

 the triangle by the summit of the cone of the 

 pleura, which ascends thus high into the 

 interval between the scaleni, interposing itself 

 between the scalenus posticus and the subcla- 

 vian artery. Towards the summit of this 

 " scalene triangle" the nervous cords which 

 constitute the brachial plexus are placed 

 along the convexity of the artery, superior 

 and external to it. 



A fleshy slip (Scalenus minimus, Scemmering) 

 is often found to pass from the scalenus an- 

 ticus to the lower, or costal extremity, of the 

 scalenus posticus ; in this course it runs be- 

 tween the roots of the brachial plexus, and 

 consequently subdivides into two the scalene 

 space. The lower compartment contains the 

 subclavian artery, the cone of the pleura, and 

 the inferior portion of the brachial plexus, 

 constituted by the seventh cervical nerve, and 

 the cord resulting from the union of the eighth 

 cervical, with the first dorsal nerve ; whilst in 

 the upper compartment (corresponding to the 

 apex of the triangle), the fifth and sixth nerves 

 of the plexus are seen to unite into a single 

 trunk. 



On the front of the scalenus anticus, and 

 separated by that muscle from the subclavian 

 artery, are found the following parts : Most 

 inferiorly the subclavian vein, lying on the 

 tendinous insertion of the muscle, and under 

 cover of the clavicle ; above the vein the 

 transverse branches of the thyroid axis, viz. 

 the supra-scapular, and the transversalis colli 

 arteries, of which the former is the more 

 inferior, whilst the phrenic nerve descends 



VOL. IV. 



obliquely inwards towards the trachcal edge of 

 the muscle, and intersects these two trans- 

 verse arteries by passing behind them. 



Superficial to all these important structures 

 is the clavicular origin of the sterno-cleido- 

 mastoid muscle. In size, shape, and direction, 

 this muscle accurately corresponds to the sca- 

 lenus anticus, which lies deeper than it, and 

 from which it is separated by the parts just 

 now stated, to lie on the front of that 

 muscle. 



The separation of the subclavian vein from 

 the subclavian artery in their second stage, 

 " constitutes one of the most remarkable fea- 

 tures in its (anatomical) history ;" this con- 

 dition is not, however, constant, for the vein 

 has been found to lie with the artery between 

 the scaleni (Blandin), and, in a few other 

 equally rare instances, the artery has accom- 

 panied the vein superficial to both muscles 

 (Manec, Quain). Lastly, the artery has been 

 seen to pass through the anterior scalenus, 

 and hence to lie in part behind and in part 

 in front of that muscle (Quain). It is to be 

 understood that these deviations from the 

 normal arrangement are remarkably infre- 

 quent. 



The anterior relations of the subclavian ar- 

 tery in its second stage, may be arranged in 

 four orders of parts : 



1. Skin, platysma, fascia. 



2. Sterno-cleido-mastoid muscle (its clavi- 

 cular origin). 



3. Subclavian vein, supra-scapular and 

 transverse cervical arteries, phrenic nerve. 



4. Scalenus anticus muscle. 



Subclavian artery in its third stage. After 

 the subclavian artery emerges from beneath 

 the scalenus anticus muscle, it inclines down- 

 wards and outwards, and thus completes the 

 arch which its entire course represents. In 

 this stage its position is marked by precise 

 limits, which are always recognisable, even in 

 the living subject. The artery, with the vein 

 and brachial plexus of nerves, which still ac- 

 company it, is here contained in the postero- 

 infenor triangle of the neck (O mo-clavicular 

 space, Velpeau), the several boundaries of 

 which are constituted by the clavicle, and by 

 the sterno-mastoid and omo-hyoid muscles. 



Whilst traversing this region the subclavian 

 artery lies at first on the scalenus posticus, and 

 then passes on the upper surface of the first 

 rib. The subclavian vein lies inferior and in- 

 ternal to the artery, and on a more superficial 

 plane than it, throughout the entire of this 

 portion of its course; it also passes with the 

 artery over the first rib. Two superficial 

 grooves in the adult bone mark the trajet and 

 relative position of these great vessels ; a tu- 

 bercle, which gives insertion to the scalenus 

 anticus muscle, separates these grooves from 

 each other (that for the artery is the more 

 posterior of the two) ; it is constantly present, 

 and serves as a guide to point out with pre- 

 cision the situation of the artery, and so assist 

 the operator to distinguish that vessel from 

 the parts which surround it. Such a guide 

 to the artery is peculiarly valuable, because, 



3d 



