of the scaleni, it would appear, instead of having, as its fellow has, a certain length of transverse course, to bend abruptly toward the arch of the aorta, becoming deeper and deeper; or, in other words, while the right subclavian has a considerable extent at its highest level, from the sterno-clavicular joint to the scalene space, the left has comparatively but a culminating point, to which it suddenly rises and from which it quickly sinks. Thus the nerves, which cross the course of the right, are nearly parallel to that of the left: and the relation of the jugular vein is similarly changed, while the subclavian vein, having a longer course than on the right side, obliquely crosses the thoracic portion of its artery.
The anatomy of the veins requires some separate notice: in crossing the scalenus anticus at its insertion, the subclavian vein is, on both sides, anterior to the artery, from which the tendon divides it, and somewhat inferior to it; the jugular vein in the upper part of the neck descends as already mentioned, beside the internal and common carotid arteries, to which it is external, similarly on both sides. The union of these veins, however, to form the venæ innominatæ 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 pneumogastric nerve, (which reflects its recurrent branch upward and inward behind the artery,) and more outwardly by the phrenic: from this point of junction the innominata vein runs toward the pericardium 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 destination, 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 innominata, just internally to the confluence which forms that trunk. On the left side it crosses the subclavian artery: on the right side it is usually, though not always, behind it.
The thoracic duct, mounting from the mediastinum, passes behind the arch, emerges between 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, superficial fascia, and platysma, and through the strong single layer of cervical aponeurosis which is fixed to the bone,—extending, if necessary, to the origin of the sterno-mastoid and to its sheath, with careful avoidance of the external jugular vein, here bending round the outer edge of the muscle,—opens a space, wherein loose cellular tissue alone veils the continuation 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 no great difficulty, and are, in fact, so long as the parts retain their normal bearings, 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 circumstances which necessitate the operation. To tie the subclavian artery for axillary aneurism may be one of the most difficult operations in surgery, involving extreme patience and much manual skill in him who undertakes it; for the disease, as it extends, not only fills the axilla, but encroaches on the neck, thrusting up the clavicle, and obliterating the interval between that bone and the omo-hyoid muscle. The operation might almost be compared 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 be guided entirely by the sense of touch, and can only apply this under the disadvantage of distance. The circumstances of such a case are well given by the late Mr. Todd of Dublin,[1] who states that, “so much was the relation of parts altered 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 accessible.” It must be under the influence of such changes that the aneurismal sac, by encroaching on the very seat of the operation, becomes liable to injury, and may, as I have witnessed, be actually transfixed by the needle. The relation of the brachial plexus is commonly 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 condition of parts is not readily to be distinguished 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 supposed arterial trunk, in the view of ascertaining its relation to the tumour, without unintentionally extending the same pressure to the subjacent artery and mis-informing one’s-
- ↑ Dublin Hospital Reports, vol. iii.
