This section is from the book "Anatomy Of The Arteries Of The Human Body", by John Hatch Power. Also available from Amazon: Anatomy of the Arteries of the Human Body, with the Descriptive Anatomy of the Heart.
The First Digital Artery, or the most internal, supplies the ulnar side of the little finger; the second advances to the cleft between the little and ring fingers; the third to the cleft between the middle and ring fingers; and the fourth to the cleft between the middle and index fingers: each of them then bifurcates to supply the opposed surfaces of the respective fingers. These digital arteries follow the anterior and lateral margins of the fingers, supplying the digital articulations and synovial sheaths, and forming a vascular plexus beneath the nail of each finger. Those of the same finger frequently communicate both in its anterior and posterior regions, and opposite the ungual phalanx meet in the form of an arch, the concavity of which looks towards the hand, and from the convexity of which are sent off numerous minute vessels to supply the extremities of the fingers. The digital nerves are superficial, that is, anterior to the arteries; the latter either pierce or cross the nerves in order to obtain this position.
It is of importance to know the precise spot at which the bifurcation of the second, third, and fourth digital arteries takes place, in order that the surgeon may avoid wounding these arteries when making the necessary incisions into the palm of the hand, for the purpose of giving exit to matter in its locality. If we examine the palm of the hand, we will find a fold or crease running somewhat transversely from one side to the other, and corresponding to the palmar surface of the metacarpophalangeal articulations of the four fingers. If we measure from this fold forwards to the lunated margin of each of the three webs between the fingers, we will find the distance of each to be from about an inch and a quarter to an inch and a half: the bifurcation of each of the digital arteries will be found to correspond to about the central point between the fold and the anterior or lunated border of the web.