1. These have in some few cases been found wanting in all, or in some of, the fingers and toes. They are very frequently absent in ill-developed supernumerary fingers and toes. When such parts coalesce, the corresponding nails unite into one plate.

There are various forms in which a preternatural number of nails exists: not only are they in excess when there are supernumerary well-developed fingers and toes, but even when a duplication of the last phalanx is but just indicated; and even without having any trace of being double, a finger or a toe sometimes has a double nail. After the loss of the terminal phalanx a new nail is sometimes formed over the second or first joint, or even upon the knuckle.

2. The size and form of the nails are subject to several congenital and acquired anomalies. Those of the latter class are particularly frequent and interesting; for from them arise the excessive growth, combined with thickening and deformity, which the nails sometimes present in a striking degree. They reach a length of several inches, become misshapen and thick, and twisted and curved like horns and talons. The principal cause of this deformity of the nails is a want of care of them, especially when to that is added neglect or inability to employ the limbs. Of other causes we are ignorant; - a remark which applies particularly to those cases in which an exuberant growth of the nails concurs with the development of horns, etc.

On the other hand, the growth of the nails is arrested in paralyzed limbs, and during the repair of fractures (Günther). They shrink too, and at the same time may be deformed or may retain their shape. When the phalangeal bones waste, the nails merely diminish in a corresponding degree; but simultaneous diminution and deformity is a state, the cause of which, and its connection with other diseases that sometimes coexist with or precede it, are still matters of conjecture. Both in old and in young persons some of the nails, and at last all of them, may lose their smoothness and polish, and cease to grow in length, while they increase in thickness. They then become dry, and split; first the upper shorter lamellae are thrown off, and at last the whole nail; and the subjacent matrix gradually assumes the nature of the other general integuments, and never produces a new nail. Sometimes the disease is limited, not indeed permanently, but yet for a considerable time, to a state in which small rugged stumps of the nail remain, together with its root: in other cases the nail withers at its lateral margins first, separates from the skin beneath, becomes everted, etc.

Again, the nails present several anomalies in respect to their form, amongst which the convex shape, in cases of extreme cyanosis, is particularly marked. In lepra, in plica polonica, in syphilis, etc, the nails are, in various ways, deformed; and newly formed nails, as is well known, are usually at first misshapen.

3. The consistence and texture of the nails are frequently altered, sometimes independently of disease of the epidermis, sometimes in consequence of it. In the above-mentioned diseases of the skin and hair more especially, they become loose, soft, succulent, and at the same time discolored, or on the contrary dry, as brittle as glass, fissured, etc.

The corium which surrounds the nail is often the seat of an acute, or of a chronic inflammation, which usually ends in suppuration and loss of the nail; and in the toes, when the nail grows in, as it is called, is now and then attended with a very considerable growth of granulations (paronychia). In some individuals the inflammation terminates in an ulceration which has the specific character of scrofula or syphilis.