2. The muscles concerned in pronation are of small capacity for work, and are not called on for sustained work. As for the muscles acting on the wrist and hand, he concludes that the extensors (carpi radialis longior and brevior, carpi ulnaris, and the extensors of the fingers) are powerful, and much exceed in capacity for work the flexors (flexor carpi radialis, flexor carpi ulnaris, the flexors of the fingers, etc.), but in all fine manual work, and specially where close grasping movements enter into association with the flexors, external strain is put upon them, whilst the flexors merely support their action. The extensor communis digitorum is the weakest of all the long finger muscles; its volume is hardly one-fourth that of the corresponding flexors, and while it acts only on the first of the phalanges, the flexors act on all three. In all fine work they are called on for heavy strain, especially the interossei and the lumbricals, but in harmony with the long flexors when grasping movements are performed. The small muscles of the fingers have nearly the same mass as the extensor communis, and in all fine movements the grasping efforts are taxed severely; but their play is under considerably more favourable physical relations than that of the extensors, whilst in addition they are aided in their work at times by the long flexors. The chief adductor muscle of the thumb (extensor metacarpi pollicis) is particularly powerful; the other extensors of the thumb are very weak, and work under unfavourable physical conditions, but are supported in their action by the strong abductor muscle. The muscles of the abductor, opponens and flexor brevis, in the complicated work thrown on the thumb in manipulation, are much exerted, so that the effects of overexertion show themselves first in this region. Thus, Edinger maintains that the muscle-supply of the arm is designed for coarse heavy work, the muscles of the fingers and the hand having to carry out more work than can be expected of them from a consideration of their volume and their physical action. The commonest form of lead palsy, the antibrachial type of Déjerine-Klumpke[5], is explicable from consideration of overexertion of the particular group of muscles named. The supinator muscle, supplied also by the musculo-spiral nerve which serves the paralyzed muscles, escapes because of its size, and the fact that functionally it belongs to the flexor group, and the first-named reason also, explain the frequent escape of the long abductor of the thumb.