ARTERIA INNOMINATA, (in human anatomy) Fr. 'front brachio-cephalique.
The innominata or brachio-cephalic artery is situated to the anterior and right side of the thorax, extending from the arch of the aorta to the sterno-clavieular articulation.
Of the three large vessels proceeding from the arch of the aorta, the innominata is the most anterior, the shortest, but of the largest calibre; it takes its origin at a point corres ponding and very nearly parallel to, the upper edge of the cartilage of the second rib almost immediately from that part of the arch of the aorta where it alters its direction from the right towards the left side, or rather from the com mencement of what is termed the transverse portion of the arch, and hence the cause of its being at this point not only to the right side but also anterior and rather superior to the other two, which arise from the remainder of the transverse division of the arch, the left carotid and subelavian arteries. It imme diately ascends obliquely upwards, outwards, and very slightly backwards, to opposite the right sterno-clavictilar articulation, where it divides into the right sub-clavian and carotid arteries, the latter of which, although the smal lest in diameter, appears from direction to be its continuation. The innominata, therefore, is but a short trunk, rarely exceeding from an inch and a half to two inches in length. Ne vertheless instances are upon record in which it has attained above two inches and a half; but these may be considered more in the light of anomalies than regular occurrences.
We now proceed to consider the various re lations which this vessel bears to the several important organs in its neighbourhood, and we shall then the more readily be able to account for the many distressing symptoms usually accompanying its enlargement. At its origin, it lies upon the trachea and at its division cor responds, although at a considerable distance, to the longus colli muscle separated from it by glands and cellular tissue. Internally, or on its left side from below upwards, are the com mencement of the left carotid artery and the trachea, the latter, however, lying upon a plane posterior to the artery, a quantity of cellular tissue and glands being usually met with between them. Externally or to its right the relations are more complicated and consist of parts of very great importance. It is here connected to the right pleura and the middle and inferior cardiac branches of the great sym pathetic nerve; the internal jugular vein lies above it and on its right side, whilst the right brachio-cephalic vein is to its right but some what anterior. Behind this vein and crossing the subclavian artery at right angles very close to its origin, we find the pneumo-gastric nerve entering the thorax and giving back its recur rent branch which winds round the subclavian artery ; still more externally is the phrenic nerve conducted into the thorax upon the an terior border of the anterior scalenus muscle, and between the two latter the internal mam mary branch of the subclavian artery. The parts covering the vessel are studied with greatest advantage from the integuments back wards; and the best method of effecting this is as follows, as it enables us at the same time to take a clear view of the attachment of the various layers of the cervical fascia to the first bone of the sternum and the inter-clavicular . ligament.
Having placed the subject with a block underneath the shoulders, and the head hanging down, thus drawing the vessel as much as possible out of the thorax, carry an incision of about five inches upwards, commencing at the middle of the sternum opposite the carti lage of the second rib. Through this incision carry another of the same length at right angles, commencing at the left sterno-clavicular arti culation, and extending along the right clavicle as far as its centre. This crucial incision should merely divide the skin, the triangular flaps of which are next to be raised and re fleeted to the right and left, thus ex sing a layer of fascia separating the skin from the platisma muscle ; this fascia is thin externally, but where it corresponds to the interval between the two sterno-mastoid muscles it becomes dense and more or less loaded with fat ; reflect this fascia and the platisma will next appear, behind which is that usually described as the superficial fascia of the neck covering the sterno-mastoid muscle, containing the external jugular vein, and increasing considerably in density above the sternum, over which it passes down in front of the pectoral muscles. Like
the previous layer its thickness is augmented by fat. If this be raised the sterno-mastoid muscles and the first layer of the deep cervical fascia, extending between their two anterior margins, are brought into view, together with some small superficial vessels and nerves. This latter fascia should be carefully examined above the sternum to the anterior margin of which it strongly adheres ; it is very dense, so much so that if we endeavour to force a finger into the thorax at this point, it effectually resists our efforts. Behind this fascia is a space cor responding in depth to the thickness of the upper edge of the first bone of the sternum, containing fat and usually a gland, and in ad dition a vein rather larger than a crow-quill, extending across the neck about half an inch above the sternum ; this communicates with a vein on either side of the neck running down on the anterior margin of the sterno-mastoid muscle, and should be carefully avoided by the surgeon in the operation for tying the in nominata, as it is of sufficient size to cause embarrassment if wounded. If the fat and gland be now removed we come down upon the second layer of this fascia, which is also very dense and adheres to the inter-clavicular ligament. Ilaving examined theseand the triangular space existing between and clavicular insertions of the sterno-mastoid muscles, the sternal insertions of the latter should be detached and the first bone of the sternum removed ; this will expose the remains of the thymus gland and the sterno-hyoid and thyroid muscles, which being cut through and reflected upwards are found to cover the deep or third layer of the cervical fascia, which may be traced from the anterior scalenus muscle to its union with its fellow of the op posite side, binding down the cervical vessels, Ste. Upon removing this fascia we come down upon the artcria innominata covered by the following parts ; inferiorly the left brachio cephalic vein passes nearly horizontally across the root of the artery to form the vena cava superior by uniting with the corresponding vein of the right side. Although the com mencement of the vena cava, strictly speaking, has a closer relation to the arch of the aorta than the innominata, it is nevertheless sufficiently near the latter to render it of considerable im portance in operations performed upon that vessel. Superiorly the first or upper cardiac nerve in its course towards the thorax crosses the innominata opposite its bifurcation ; we next observe the right inferior thyroid vein, which, emanating from the lower portion of the thyroid gland, and having formed with its fellow of the opposite side the thyroid venous plexus runs, obliquely downwards from the gland towards the right side directly in front of the innominata artery, and empties itself into the vena cava superior between the two brtchiu-cephalic veins. The middle thyroid artery, when it exists, may now be seen ascend ing in front of the trachea. These several objects, viz. the left brachio-cephalic and thy roid veins with the cardiac nerve, are all en veloped in a quantity of loose cellular tissue and glands serving to connect them to the vessel, which may now be fully exposed and its different relations studied ; when we shall observe that on its right side there is a space bounded superiorly by the right subclavian artery, inferiorly by the left brachio-cephalic vein, to the right by the right brachio-cephalic vein, and to the left by the innominata artery itself; this is the situation where the aneurismal needle should be introduced in the operation for tying this vessel, as we thus run less risk of wounding the veins.