SUBCL AVIAN ARTERIES (Artericc subclaviec, Lat. ; Arteres sous-clavieres, Fr. ; die Schliissclbein Pulsadern, Germ.). — These arteries, two in number, are the great vessels destined to supply the upper extremities with blood. Each passes to the corresponding ex tremity as a continuous trunk, which in its course gives off numerous collateral branches to the larynx, neck, nervous centres, thorax, &c.
The subclavian arteries on the right and left sides respectively differ from each other in their origin, length, direction, and in their relations to surrounding parts,—differences, however, which occur in the first stage of these vessels only : thus, on the right side, the • subclavian artery is derived from the Arteria innominata, and on the left from the arch of the aorta ; but on both sides alike the lower or outer margin of the first rib marks the termination of each vessel, which, in its further course towards the upper extremity, is designated by the name of Axillary.
The course of each subclavian artery may, in general terms, be described as representing an arch, the convexity of which looks upwards towards the neck, whilst the concavity has an aspect downwards, and corresponds closely to the apex of the lung. On the right side the extremities of this arch are nearly on the same level, the outer, however, passing a little lower clown than the inner ; whilst on the left side the reverse obtains, the inner (or cardiac) extremity of the arch of the left subclavian artery, which springs from the aorta, being on a much lower level than the outer. Owing to the difference in the origin of these vessels, the left subclavian artery has a stage within the thorax, which does not belong to the artery of the right side.
The subclavian artery on each side is ac companied by a vein of large size ; the direction of the vein is much more transverse than that of the artery, so as to resemble in some respect, as Cruveilhier expresses it, " the cord of the arc which the artery describes :" the subclavian vein is consequently the shorter vessel of the two.
The course of each subclavian artery may be divided into three stages, to which the ma jority of anatomists agree in assigning the following limits :— A first stage comprises that portion of the vessel, from its origin, to the inner, or tracheal edge, of the scalenus anticus muscle.
A second stage includes so much of the artery as is contained between the sca leni muscles ; and the Third stage extends from the acromial edge of the scalenus anticus muscle to the lower or outer margin of the first rib at this latter point the axillary artery commences.
According to some anatomists (as Bichat), the outer margin of the scaleni muscles is the limit between the subclavian and axillary vessels ; others (as Cruveilhier) insist upon the clavicle as the line of demarcation between these two great trunks ; but the stages above assigned to the subclavian arteries are strictly in accordance with the views of British ana tomical authorities.
The subclavian vein may be divided into two stages, which correspond to the second and third stages of the artery ; at the inner edge of the scalenus anticus muscle on each side of the neck, the subclavian joins the in ternal jugular vein to form the vena inno minata (of Meckel), which latter vein conse quently corresponds to the first stage of the subclavian artery.
As the right and left subclavian arteries differ from each other essentially in their first stage, it is necessary to describe them sepa rately in this portion of their course.
First stage of the right subelavian artery. —This portion of the vessel varies from one to two inches in length ; it extends from the summit of the arteria innominata to the tra cheal edge of the anterior scalenus muscle, and passes in a direction outwards, and slightly upwards. At its commencement it lies to the right of the trachea, and is concealed by the sterno-clavicular articulation.