THE SKIN AND ITS APPENDAGES. 265 



cleft and converted into one of the compound variety. The 

 papillae of the hand and the foot are distributed in characteristi- 

 cally-arranged rows, which form elaborate, and for each individual 

 constant and distinctive, ridges on the integumentary surface. These 

 ridges have been found to retain their definite arrangement, or 

 "patterns," from early life to old age unchanged. This constancy 

 in the details of the surface markings has been taken advantage of 

 in securing records by means of impressions for the purposes of 

 identification. 



Non-striped muscular tissue occurs within the corium in con- 

 nection with the hair-follicles, as the arrectores pilorum, and in the 

 subcutaneous tissue, attached to the under surface of the corium, 

 in particular localities, as in the scrotum, the perineum, the penis, 

 and in and around the nipple. 



The subcutaneous stratum consists of a reticular framework of 

 loosely-disposed fibro-elastic bundles continued from those of the 

 deeper layers of the corium without sensible interruption ; the inter- 

 fascicular spaces are largely occupied by adipose tissue, which 

 in many places forms a compact layer, the panniculus adiposus. 

 The cellular elements of the subcutaneous tissue are the usual cells 

 of connective tissue, including fusiform and plate-like elements, 

 leucocytes, and fat-cells : while the latter are quite constant con- 

 stituents of the deeper layers of the skin, within the integument of 

 the eyelids, the penis, and the labia minora fat does not occur. 



THE APPENDAGES OF THE SKIN. 



These include the nails and the hairs, together with the cutane- 

 ous glands, all of which are directly derived from the ectodermic 

 epithelium of the epidermis. 



THE NAILS. 



Each nail consists of a large exposed body, which ends ante- 

 riorly in the projecting free edge, and extends posteriorly as the 

 root some considerable distance beneath the overhanging upper 

 margin of the groove, or nail-fold, receiving the root ; at the sides 

 the borders of the nail are covered by the nail-walls. The nail, 

 which represents an enormously developed stratum lucidum, rests 

 upon a highly vascular and sensitive nail-bed, the posterior portion 

 of which, covered by the root of the nail, is the matrix. The nail- 

 root is usually lighter in color and somewhat opaque, owing to the 

 thickness of the stratum Malpighii ; on the thumb it extends beyond 

 the nail-fold as a pale projecting convex area, the lunula. 



While attached throughout the extent of the nail-bed, the growth 

 of the nail takes place from the matrix alone, each newly-formed 



