The deformity is bilateral and symmetrical in nearly a third of the cases, in the rest having a slight preference for the right side, in the proportion of five to four. It is usually localised in the first inter-phalangeal articulation, but occasionally implicates both inter-phalangeal joints, or the distal joint only. _Symptoms._—The stages of the deformity in a typical case may be described as follows: In the _first_ period, which is rarely seen by the surgeon, the toe is slightly extended at the metatarso-phalangeal articulation, and flexed at the proximal inter-phalangeal joint. By passive movement the flexed joint may often, but not always, be extended; but the range of motion, even in the early stage, is found to be less than that of the neighbouring or opposite toe. The distal joint is usually unaffected, and may be held straight or slightly flexed, but occasionally it undergoes contraction, either alone or in association with the proximal articulation. There is no evidence at this or any subsequent time of inflammation in or around the joint structures, except in association with corns or bursæ. How long this period may last it is difficult to say, as it may altogether escape the notice of the patient. In the _second_ stage the flexion of the inter-phalangeal joint becomes more pronounced, and the secondary extension at the metatarso-phalangeal joint increases _pari passu_. At this period the affected articulation is fixed for all movement of extension, but the power of flexion within the limits left to it remains unimpaired; in other words, the angle may be diminished, but not widened, and the toe, although contracted, is neither ankylosed nor paralysed. In exceptional instances the flexion may be overcome by strong passive force, and a distinct trigger-like action established, the middle phalanx becoming extended and flexed again with a movement very comparable to that which takes place during the opening and shutting of the blade of a pocket-knife. As secondary results of the contraction of the proximal inter-phalangeal joint the patient is subject to certain inconveniences which may give rise to much suffering, and are usually the immediate cause of his appeal to the surgeon. The chief of these are a bursal formation, which is very liable to inflammation, over the angle of flexion, and two associated callosities, one above the head of the retracted phalanx, the other beneath the head of the metatarsal bone, both consequent upon the pressure exercised by the boot. (See Fig. 10.) A third callosity may develop over the tip of the toe, and the soft parts over the terminal joint may become somewhat swollen, so that the digit presents a clubbed appearance. The degree of interference with functions and comfort varies greatly in different cases, partly in relation to the degree of the contraction and partly to the sensibility of the patient. In some persons a hammer toe of a marked kind will cause