The superficial palmar arch, F, Plate 17, lies beneath the dense palmar fascia; and whenever matter happens to be pent up by this fascia, and it is necessary that an opening be made for its exit, the incision should be conducted at a distance from the locality of the vessel. When matter forms beneath the palmar fascia, it is liable, owing to the unyielding nature of this fibrous structure, to burrow upwards into the forearm, beneath the annular ligament D, Plates 17 and 18. All deep incisions made in the median line of the forepart of the wrist are liable to wound the median nerve B, Plate 17. When the thumb, together with its metacarpal bone, is being amputated, the radial artery E, Plate 19, which winds round near the head of that bone, may be wounded. It is possible, by careful dissection, to perform this operation without dividing the radial vessel. DESCRIPTION OF PLATES 17, 18, & 19. PLATE 17. A. Radial artery. B. Median nerve; b b b b, its branches to the thumb and fingers. C. Ulnar artery, forming F, the superficial palmar arch. D. Ulnar nerve; E e e, its continuation branching to the little and ring fingers, &c. G. Pisiform bone. H. Abductor muscle of the little finger. I. Tendon of flexor carpi radialis muscle. K. Opponens pollicis muscle. L. Flexor brevis muscle of the little finger. M. Flexor brevis pollicis muscle. N. Abductor pollicis muscle. OOOO. Lumbricales muscles. P P P P. Tendons of the flexor digitorum sublimis muscle. Q. Tendon of the flexor longus pollicis muscle. R. Tendon of extensor metacarpi pollicis. S. Tendons of extensor digitorum sublimis; P P P, their digital prolongations. T. Tendon of flexor carpi ulnaris. U. Union of the digital arteries at the tip of the finger. [Illustration: Right hand, showing blood vessels, muscles and other internal organs.] Plate 17 PLATE 18. A. Radial artery. B. Tendons of the extensors of the thumb. C. Tendon of extensor carpi radialis. D. Annular ligament. E. Deep palmar arch, formed by radial artery giving off e, the artery of the thumb. F. Pisiform bone. G. Ulnar artery, giving off the branch I to join the deep palmar arch E of the radial artery. H. Ulnar nerve; h, superficial branches given to the fingers. Its deep palmar branch is seen lying on the interosseous muscles, M M. K. Abductor minimi digiti. L. Flexor brevis minimi digiti. M. Palmar interosseal muscles. N. Tendons of flexor digitorum sublimis and profundus, and the lumbricales muscles cut and turned down. O. Tendon of flexor pollicis longus. P. Carpal end of the metacarpal bone of the thumb. [Illustration: Left hand, showing blood vessels, muscles and other internal organs.] Plate 18 PLATE 19. AAA. Tendons of extensor digitorum communis; A*, tendon overlying that of the indicator muscle. B. Dorsal part of the annular ligament. C. End of the radial nerve distributed over the back of the hand, to two of the fingers and the thumb.