From calx, the heel, or calco, to tread; because it used to be applied to the thick skin at the bottom of the heel, hardened by pressure; but it is a cutaneous or osseous hardness, either natural or preternatural. Generally it means the callus generated about the edges of a fracture. Sometimes it means a com on the toes, the hardness in the hands produced by labour, or the hard edges of ulcers. See Bell's Surgery, ii. 326. Kirkland's Med. Surgery, ii. 246.
This term and callositas are, in a special sense, spoken of the eye lids, both by Galen and Scribonius Largus; and callus has a particular signification, in which it means the corpus callosum of the brain. Paracelsus gives the name of callus to an abscess, or ulcer, caused by acrid juices which excite violent itching. For callus on the hands and feet see Clavus.
The retraction of the part divided is a common symptom in wounds; and the stronger the contractile force, the more the sides of the wound recede from each other. The skin of the head is thick and strong, and equally tense on all parts of the skull, and under it lays a cellular membrane; so that when the skin of the cranium is divided, the lips of the wounds are far retracted, and are called callus, consequently wounds of the forehead generally leave large scars behind them.
As the growing vessels in wounds of the soft parts are tender in consequence of their not being pressed by the skin, they may degenerate into fungous flesh. The same holds true in the callus of the bones, which may-become luxuriant when the vessels which constitute the substance of the growing bone are distended, either by a redundance, or too strong impetus of the fluids.
Dr. Nisbet and Dr. Hunter imagine a callus of the bone is not formed by the inspissation of any fluid, but from a regeneration, or, as it were, granulation from the fibres of the bone.