It may considerably facilitate finding the artery in the living subject, to bear in mind the superficial indices of its course : and from what has been already stated it may be gather ed, that in the upper half of this region the vessel is situated in a triangular hollow, whose base is the brachialis anticus in the lower part of the arm, whose outer side is the RI pinator longus, and whose inner side is the pronator teres. In the lower portion it oc cupies a linear and comparatively shallow de pression, between two tendons whose 'margins the fingers readily recognise through the skin, viz. that of the supinator longus externally, the flexor carpi radialis internally. A line, therefore, from the inner border of the biceps tendon, to the inferior apex of the triangle, indicates with tolerable accuracy the first subdivision of its course ; while another from this point, parallel and equidistant to the two tendons above named, marks it in the remain der of the forearm.
(b.) In the wrist.— This part of the artery is considerably shorter than the preceding, being scarcely one fifth of its length : its di rection is downwards and outwards from the front of the forearm to the back and lower part of the wrist. In this course, the vessel lies on the external lateral ligament of the wrist joint, and at its termination on the pos terior ligament of the sanie articulation ; and corresponds to the scaphoid and trapezium bones which are beneath these. It is covered by skin and fascia, and at first situated at some distance from the surface, becomes to wards its termination considerably rnore su perficial. In its course it is crossed obliquely by three tendons : in the first instance by two of these placed closely side by side, the extensores ass's metacarpi and prima internodii pollicis ; but by the third, the extensor se cundi internodii, only just before the artery enters the palm : so that between these two crossings, the vessel runs obliquely downward in the bottom of a groove, which is bounded on each side by these tendons. and whose depth is greatly increased by the action of the muscles with which they are continuous. It finally leaves the back of the hand, by passing between jhe processes of origin of the abduc tar indicis.
(c.) In the palm. — The vessel having per forated the metacarpal space, is situated very deeply in the palm of the hand, beneath the flexor brevis pallicis and the different struc tures superficial to this muscle ; namely, the tendons of the flexores sublimis and profundus digitorum, with the lumbricales muscles, the branches of the median nerve, and, above these, the palmar fascia and integuments. Immediately giving off its magna pollicis and radialis indicis branches, it now crosses the palm as the deep palm,. arch, or " palmaris
profunda," which, slightly convex forwards, lies on the proximal extremities of the meta carpal bones, and on the interossei muscles between them ; being directed at right angles to them towards the inner side of the hand, and joined in the fourth metacarpal space by the communicating branch of the ulnar, which completes the arterial circle. This latter part is of course uncovered by flexor brevis pol licis, and, just at its junction with the com municans ulnw, it might almost be considered as covered by the flexor brevis minimi digiti.
Branches of the radial artery.— Amid very numerous ramifications, the following are those whose constancy and size require a separate mention.
(1.) Arteria radialis recurrens.— This large branch is given off from the outer side of the radial trunk almost immediately upon its origin from the brachial artery, and whilst it is contained in the triang,ular hollow before referred to. It passes at first downwards, then outwards, and finally upwards ; lying on the supinator brevis and brachialis anticus successively ; and then occupying the groove between the biceps and supinator radii longus muscles, but overlapped by the latter, it ter minates in the arm by anastomosing with the superior profunda, which descends to meet it after passing beneath the outer head of the triceps. It has thus a curved course, the convexity of which is directed downwards towards the wrist. Its branches are very numerous, and chiefly supply the muscles with which it is in contact, mosculating with the vessels which they derive from other sources, and with the superior profunda as aforesaid.
(2.) Arteria supetficialis voles', which usually comes off from the artery just as it leaves the lower border of the radius to turn around the wrist; and, directed ahnost vertically down wards, proceeds over the annular ligament and immediately beneath the integuments, until it arrives at the muscles of the thenar eminence ; amongst or upon -which it passes, crossing them at an oblique angle, to „join the termination of the palmar artery, or, in other words, to complete the superficial palmar arch. Liable to very considerable though un important deviations in its exact position, perhaps one of the most constant is that where the abductor pollicis lies over the ves sel, itself placed upon the flexor brevis and opponens muscles. Its varieties in point of size are chiefly connected with the relative proportions of the other arteries, and are de ferred to them ; but it is usually a very small branch, and, quite as frequently as not, ends in these muscles without any direct junction with the superficial palmar arch.