Each of the subclavian arteries in its third stage takes a direction obliquely downwards and outwards, and having arrived at the lower margin of the first rib changes its name, and becomes the axillary artery. In this course it is covered anteriorly by the clavicle and subclavian muscle, immediately above which it has other important relations, which we may now proceed to study. On raising the integuments, platysma, and fascia, together with some of the supra-clavicular branches of the cervical plexus of nerves, from off the front of the artery, we usually observe a space between the trapezius muscle on the outside, and the sterno-mastoid on the inside : in some cases, however, the fibres of these muscles meet at their clavicular attachments, so that in order to expose the artery it becomes necessary to divide transversely some of the fibres of the trapezius. In the deeper layer or stratum, we observe the posterior belly of the omo-hyoid muscle passing at first horizontally inwards, and then slightly upwards and inwards towards the larynx. A triangular space is thus formed, bounded inferiorly by the clavicle, internally by the posterior margin of the sterno-mastoid muscle, and externally by the posterior belly of the omo-hyoid; in this space, which is called the posterior inferior lateral triangle of the neck, the artery may be felt emerging from behind the scalenus anticus muscle accompanied by the brachial plexus of nerves. If we were to judge of the size of this space by the appearance it presents in the dissected subject, we would be led into great error. It is, in fact, hardly appreciable while the muscles which bound it preserve their natural relative position, though dissection may make it appear of considerable extent. The brachial plexus lies behind the artery, but a large portion of it projects at its outer or acromial side. The vein is situated on a plane anterior to the artery, but inferior and nearer to the middle line. The anterior thoracic nerve begins to descend in front of it in the lower part of this stage; and lastly, it is crossed anteriorly by the transversalis humeri artery, which runs in this situation nearly parallel to the clavicle. Posteriorly it rests on part of the scalenus posticus, on the inferior fasciculus of the brachial plexus, on the origin of the middle thoracic nerve, which supplies the lesser pectoral muscle, and on the first rib. In operations on the axillary artery and about the shoulder, the artery may be easily compressed.

Ligature Of The Subclavian Artery In The First Stage

Professor Colles's Case

The ligature was passed round the artery, but not tightened till the fourth day, great dyspnoea and oppression about the heart having occurred. On the ninth day the patient complained of sensation of strangling and pain about the heart. He then became delirious, and died in a few hours.*

Mr. Hayden's Case

" Eliza Moulang, aged 57, unmarried, and of intemperate habits, states that in November, 1834, she perceived a small pulsating tumor, of the size of a pea, about an inch and a half below the right clavicle, and at an equal distance from the sternum. In April, 1835, it had increased to the size of a marble, and was for the first time attended with pain, which was of against the rib for the purpose of preventing hemorrhage.

* Edin. Med. and Surg. Jour., 1815.