. Quain's elements of anatomy . terior edge, that is, allround the margin of the groovein which the nail is lodged;« in front the cuticle of the point of the finger becomescontinuous with the under surface of the uail a little way behind itsfree edge. The nail, like the cuticle, is made up of epithelial cells. The oldest andmost superficial of these are the broadest and hardest, but at the sametime very thin, and so intimately connected together that their respec-tive limits are scarcely discernible. They form the exterior, horny jxirtof the nail, and cohere together in irregular layers, so as
. Quain's elements of anatomy . terior edge, that is, allround the margin of the groovein which the nail is lodged;« in front the cuticle of the point of the finger becomescontinuous with the under surface of the uail a little way behind itsfree edge. The nail, like the cuticle, is made up of epithelial cells. The oldest andmost superficial of these are the broadest and hardest, but at the sametime very thin, and so intimately connected together that their respec-tive limits are scarcely discernible. They form the exterior, horny jxirtof the nail, and cohere together in irregular layers, so as to give thispart a lamellar structme. On the other hand, the youngest cells, whicharc those situated at the root and under siuface, are softer and of arounded or polygonal shape. The deepest layer differs somewhat fromthe others, in ha^vang its cells elongated, and arranged perpendicularly,as in the case of the epidermis. Thus the under part of the nail (, b) corresponds in nature with the Malpighian or mucous layer of. HAIES. 245 the eioidermis, and tlie upper parfc (c) with the horny layer. As in thecase of the epidermis, the hardened scales of the nails may be made to re-assmne their cellular character by treatment with caustic alkah, and after-wards with water ; and then it is seen that they still retain their growth of the nail is effected by a constant generation of cells atthe root and under surface. Each successive series of these cells beingfollowed and pushed from their original place by others, they become flat-tened into diy, hard, and inseparably coherent scales. By the additionof new cells at the posterior edge the nail is made to advance, and bythe apposition of similar particles to its under surface it gTows in thick-ness ; so that it is thicker at the free border than at the root. The nailbeing thus merely a modified and exuberant part of the epidermis, thequestion at one time raised, whether that membrane is continued under-neath it, loses
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Keywords: ., boo, bookcentury1800, booksubjectanatomy, booksubjecthumananatomy
