The anatomy of the veins requires some sepa rate notice: in crossing the scalenus anticus at its insertion, thesubclavianvein is, on both sides, anterior to the artery, from which the tendon di vides it, and somewhat inferior to it; the jugular vein in the upper part of the neck descends as already mentioned, beside the internal and com mon carotid arteries, to which it is external, similarly on both sides. The union of these veins, however, to form the vense innominatm differs in the following manner. On the right side, the jugular vein, inclining from its artery below, joins the subclavian on the insertion of the scalenus anticus : the arrangement of these important parts is such that they form together an elongated triangle, of which the carotid artery is the inner side, the jugular vein the outer, and the first stage of the subclavian the base, here crossed at a right angle by the pneurnogastric nerve, (which reflects its recur rent branch upward and inward behind the artery,) and more outwardly by the phrenic : from this point of junction the innominata vein runs toward the pericardiuin on the pulmonic side of its artery, that is, externally to it and on an inferior plane. On the opposite side the jugular vein, anticipating its ultimate destina tion, obliquely bends toward the right side, overlapping the carotid artery, in front of which it receives the subclavian vein by its outer side : the resulting vena innominata sinistra runs almost transversely across the arch to join its fellow at the right extremity of this. The vertebral vein opens into the innotninata, just internally to the confluence which forms that trunk. On the left side it crosses the sub clavian artery : on the right side it is usually, though not always, behind it.
The thoracic duct, mounting from the medi astinum, passes behind the arch, emerges be tween the carotid and subclavian arteries in the root of the neck, and, curving abruptly downwards, outwards, and forwards, crosses the latter artery and discharges its contents by a valvular opening into the subclavian vein close to the angle of its confluence with the jugular.
The surgical relations of this region regard the subclavian artery and the operations which are practised on it. Of these the most usual Is its ligature on the outside of the scalene space, where lying upon the upper surface of the rib. An incision, corresponding to the middle of the clavicle, through the skin, super ficial fascia, and platysma, and through the strong single layer of cervical oponeurosis which is fixed to the bone,—extending, if neces sary, to the origin of the sterno-mastoid and to its sheath, with careful avoidance of the ex ternal jugular vein, here bending round the outer edge of the muscle,--opens a space, where in loose cellular tissue alone veils the conti nuation of the pre-vertebral fascia, which is prolonging itself from the scaleni around the subclavian vessels : a division of this lamina, as near as possible to the costal attachment of the scalenus anticus, completes the exposure of the artery, which is recognised by the finger, as it emerges from behind the tendon of that muscle, in immediate contact with the rib.
The steps of the operation thus considered seem of TIO great difficulty, and are, in fact, so long as the parts retain their normal bear ingi, of extremely easy performance : the artery is at an inconsiderable depth ; its relations are singularly definite and unembarrassed. But such is not their practical facility, under cir cumstances which necessitate the operation. To tie the subclavian artery for axillary aneu rism may be one of the most difficult opera tions in surgery, involving extleme patience and much manual skill in him vt.ho undertakes it ; for the disease, as it extends, not only fills the axilla, but encroaches on the neck, thrust ing up the clavicle, and obliterating the in terval between that bone and the omo-hyoid muscle. The operation might almost be com pared to one of tying the axillary artery in its normal relations from above the clavicle. It lies at the bottom of a deep and narrow cavity, in which the operator must he guided entirely by the sense of touch, and can only apply this under the disadvantage of distance. The cir cumstances of such a case are well given by the late Mr. Todd of Dublin,* who states that, " so much was the relation of parts al tered by the magnitude of the tumour and consequent elevation of the clavicle, that the omo-hyoid was situated an inch below this bone, and it was found necessary to draw it up from its concealment, and to cut it across, that the subjacent parts might become acces sible." It must be under the influence of such changes that the aneurismal sac, by en croaching on the very seat of the opemtion, becomes liable to injury, and may, as I have witnessed, be actually transfixed by the needle. The relation of the brachial plexus is com monly such that it lies on a plane posterior to the artery, and for the greater part above it ; occasionally, however, its last root passes in front of the vessel, and in the disguised con dition of parts is not readily to be distin guished from it ; since the touch fails in its ordinary discrimination, where exercised with so much difficulty, and it is hardly practicable to apply the test of compression to the sup posed arterial trunk, in the view of ascertain ing its relation to the tumour, without un intentionally extending the same pressure to the subjacent artery and mis-informing one's self accordingly. It must have been through these means of fallacy that I have seen a most cautious and experienced operator de ceived : he compressed the supposed ar tery, mised on the aneurism-needle, with his finger; the pulsation ceased, the ligature WIIS tightened, and the severe pain occa sioned by this step at once declared the error (which was in the course of a few moments remedied, and the operation ultimately and entirely successful); the convexity of the nee dle was doubtlessly resting on the artery, and compressed it upon the surface of the rib.