The brachial or humeral artery, [a. brachialis], the continuation of the axillary, is placed along the inner and anterior aspect of the arm, extending from the lower border of the axilla, that is, of the tendons of the latissimus and teres major, to about a finger's breadth below the bend of the elbow, or opposite the neck of the radius, where it divides into the radial and ulnar arteries.
The vessel gradually inclines from the inner side to the fore part of the limb, and its direction may be marked out by a line drawn from midway between the folds of the axilla to the middle point between the condyles of the humerus. From the position it bears with reference to the bone, it will be inferred that to command the flow of blood through the artery at its upperpart, pressure should be directed outwards, while over the lower end of the vessel the pressure should be made from before backwards. The position of the artery in the greater part of its course is also indicated by the depression along the inner border of the coraco- brachialis and biceps ; and, except at the bend of the elbow, or where it is slightly overlaid by those muscles in the arm, it may be said to be superficial in its whole extent. It can be laid bare without dividing any muscular fibres.
The brachial artery is covered by the integument and fascia of the arm as far as the bend of the elbow, where it sinks deeply in the interval between the pronator teres and supinator longus muscles, and is covered by the fibrous expansion given from the tendon of the biceps to the fascia of the fore-arm. It rests at first on the triceps muscle, — the musculo-spiral nerve, however, and the superior profunda artery intervening, — then crosses over the insertion of the coraco-brachialis muscle, and lies from thence to its termination on the brachialis anticus. At its outer side the artery is in apposition with the coraco- brachialis, and afterwards and for the greater part of its length with the biceps, the inner border of one or both muscles sometimes slightly overlapping it.
The basilic vein is placed over the brachial artery, (its lower half, sometimes its whole length,) except at the bend of the arm, where the median basilic occupies the same position with respect to the artery. Only the fascia, or opposite the elbow-joint, the expansion from the tendon of the biceps, is interposed between the vein and artery. Venae comites are in close contact with the artery, short transverse branches of communication passing from one to the other, so as at many points to encircle it.
The median nerve follows closely the course of the artery, lying immediately in front of it in the greater part of the arm ; at the axilla this nerve is somewhat to the outer side of the vessel, but at the elbow it lies to the inner side, both being on the same plane, supported by the brachialis anticus muscle. The nerve usually crosses in front of the artery, but in some instances behind it. — Of the large branches of the brachial plexus which are closely connected with the axillary artery, none continue in the immediate neighborhood of the brachial artery along the arm, except the median. The external cutaneous and circumflex separate at once from the vessel in the axilla, the musculo-spiral turns back immediately below the axilla, and the internal cutaneous and the ulnar incline gradually inwards from the vessel, — or perhaps more properly the vessel turns outwards from the nerves.
From Quain's Anatomy.