surmounted, the movement is terminated by a sudden spring-like action of the extensors or flexors, as the case may be. This condition undoubtedly exists in certain cases of hammer toe and hammer finger; but it must be recollected that these two affections are developmental, and always begin during the period of active growth; while the great majority of examples of trigger finger appear in adult life, after the osseous and ligamentous elements of the articulation have assumed their permanent form. Corresponding changes of form, however, might occur in rheumatoid arthritis. (4) The development on the side of the head of the proximal bone of an osseous excrescence, so placed that the narrow (proximal) attachment of the lateral ligament must pass over it during the movements of flexion and extension. The possibility of this condition, suggested on theoretical grounds by Poirier, cannot be denied; it is, in fact, normal in the tibio-tarsal joint of the ostrich; but its existence in the human subject has yet to be demonstrated. It might well appear in connection with rheumatoid arthritis, but indications of this disease are found in only a small proportion of cases of trigger finger. (5) Spastic irregularities of muscular action. According to this view, advanced by Carlier, the muscle at fault is nearly always the flexor sublimis. It must be recollected that the flexion of the first phalanx is effected mainly by the interossei and lumbricalis, that of the second principally by the flexor sublimis, and that of the third entirely by the flexor profundus; the extension of the first phalanx is due to the common extensor aided by the special accessory extensors in the case of the index and little fingers; the corresponding movement of the second and third phalanges is accomplished by the interossei and lumbricales. In the thumb the metacarpo-phalangeal joint is acted upon by the long and short flexors in the one direction, and by the extensores primi et secundi internodii in the other, while the distal phalanx is flexed by the long flexor and extended principally by the abductor and flexor brevis, which send expansions to the long flexor tendon. If, then, we assume the existence of a reflex spasm of the flexor of a joint the resistance must be overcome by vigorous action of the extensors, or by passive force; and if under these circumstances the spasm yield suddenly the spring phenomenon might be closely simulated. The theory is ingenious, but it involves certain difficulties in its application to trigger finger in general: first, that the “spring” ought to be confined to the movement of extension, unless we assume—and this perhaps is too much to ask—that a similar spasm may affect the extensor also, and be overcome in an analogous way; secondly, that the spring movement should be greatly altered when the tendon of the sublimis is relaxed by flexion of the wrist and metacarpo-phalangeal joint, a modification that has not yet