SKIN AND ITS APPENDAGES. 149 



down their tissue ; these reagents, therefore, are useful 

 in bringing out their details of structure. Tactile 

 corpuscles are best found in sections of the skin of the 

 palmar surface of the third phalanges of the fingers, 

 and in the corresponding portions of the toes. 



SECT. II. NAILS. The substance of the nails is 

 nothing more than a peculiar form of hypertrophy 

 of the epidermis. The deep surface of this horny 

 plate rests directly upon the true skin ; its anterior 

 margin is free, whilst its posterior and lateral borders 

 are received into a groove formed by a fold of the 

 true skin (PL XXIV. fig. I. II. IIL). ' 



On the surface of the derma, in contact with the Matrix. 

 deep surface of the nail, known as its matrix, we 

 find numerous delicate ridges which run parallel with 

 each other and with the axis of the limb, converging 

 at the root of the nail towards a common centre, and 

 usually possessing no papillae. With these exceptions 

 the structure of the matrix of the nail is the same as 

 that of the true skin elsewhere ; its two strata exist 

 as usual ; it is to be noticed, however, that its vascu- 

 lar network is less rich towards the root of the nail, 

 causing a dead white surface of the semilunar shape 

 (the lumda) partly covered by the margin of the 

 fold of the skin, into which the posterior border of 

 the nail is received. 



It consists of both of the layers of which the skin 

 is formed, but the dermal layer is destitute of papil- 

 Ise (fig. I. 5). 



In the nail we find a repetition of the three strata structure of 

 of cells which we have seen forming the epidermis. 

 The middle and deep layers are identical with those 



