“_Hammer finger_” (Fig. 6) is not a rare complaint, although much less familiar, possibly because much less troublesome, than hammer toe. It may be defined as a permanent flexure of one or more digits, nearly always at the first or second inter-phalangeal joint, and unassociated with inflammatory or degenerative disease in the articular structures, or with any evidence of paralytic or spastic phenomena in the muscles. It is strictly limited in onset to the developmental period, and may manifest itself at any time between birth and adult life, possibly even before birth in some instances. It is more common in girls than in boys. The digit most frequently attacked is the little finger, and the proximal inter-phalangeal joint is more often affected than the distal joint. It is usually symmetrical. The contraction is slow, progressive, and painless, and becomes arrested spontaneously at any degree of flexion, but seldom goes beyond an angle of 90°. The joint cannot be extended by any ordinary force except in the earliest stage, and even then the bent position is immediately resumed after the cessation of the effort. Flexion, on the other hand, is complete and of fair power. No alteration is produced in the deformity by flexion of the wrist, a fact which proves that the main obstacle to extension does not lie in the tendons. There are no contracted fascial bands, and, as a rule, the skin is normal, but occasionally a small longitudinal fold may be present in the angle of flexion. In rare instances the resistance to extension is capable of yielding suddenly with a spring-like action, and a similar movement recurs as the joint is replaced in the position of flexion. These cases are usually classed with the condition known as “trigger finger.” The contraction also occurs in the metacarpo-phalangeal joint, but very rarely attains a degree marked enough to attract the attention of patient or surgeon. In 800 children examined at the Central District School at Hanwell by Dr. Litteljohn and myself, this affection was found seven times—five times in girls, twice in boys, the ages of the subjects ranging between eight and fourteen. In all these the deformity was confined to the little finger, and in six cases it was bilateral. The proximal inter-phalangeal joint was affected in ten, and the distal joint in three of the thirteen digits. The angle of flexion measured from the prolonged metacarpal axis, ranged between 20° and 80° in the different cases. A contraction of less than 20° was frequent, but the deformity was so slight that the cases were not recorded as pathological. Besides these examples, I have met with several cases in adult women, in whom the defect is said to have originated in early childhood. The little finger was affected in all, but in one the ring finger, and in another the ring and middle fingers were also involved. Only the last was unilateral. The following case may serve as a type of the more troublesome forms: