(kla'-vus) [L., " a nail; a wart; a corn"]. Corn; a hyperplasia of the horny layer of the epidermis, in which there is an ingrowth as well as an outgrowth of horny substance, forming circumscribed epidermal thickenings, chiefly about the toes. Corns may be hard or soft, the latter being situated between the toes, where they are softened by maceration. Both forms are due to pressure and friction. C. hystericus, a pain in the head, as if a nail were being driven in. * Claw-foot. A form of talipes due to depression of the heads of the metatarsal bones, with forced extension of the first phalanges and flexion of the last; it is a result of paralysis of the interossei and lumbricales muscles and of those inserted into the sesamoid bone of the great toe. * Claw-hand. A condition of the hand character- ized by overextension of the first pha- langes and extreme flexion of the others. The condition is a result of atrophy of the interosseous muscles, with contraction of the tendons of the common extensor and long flexor. Syn., Main-en- griffe. * Clearing Agent. A substance used in micro- scopy to render tissues transparent and suit- able for mounting.