I have already had occasion to point out the structure of the integuments, considered in their mechanical office of protecting the general frame of the body; but we are now to view them in their relation to the sense of touch, of which they are the immediate organ. It will be recollected that the corium forms the principal portion of the skin; that the cuticle composes the outermost layer; and that between these there occurs a thin layer of a substance, termed the rete mucosum. The corium is constructed of an intertexture of dense and tough fibres, through which a multitude of blood vessels and nerves are interspersed; but its external surface is more vascular than any other part, exhibiting a fine and delicate net-work of vessels, and it is this portion of the skin, termed by anatomists the vascular plexus, which is the most acutely sensible in every point: hence, we may infer that it contains the terminations of all the nervous filaments distributed to this organ, and which are here found to divide to an extreme degree of minuteness.

When examined with the microscope, this external surface presents a great number of minute projecting filaments. Malpighi first discovered this structure in the foot of a pig; and gave these prominences the name of papillœ.