THE 8KIN AND ITS APPENDAGE v 91 



may be found. It is called the stratum luridnm. (4) As these cells suc- 

 cessively approach the surface by the development of fresh layers from beneath, 

 they assume a flattened form from the evaporation of their fluid contents, 

 and consist of many layers of horny epithelial scales in which no nucleus is 

 discernible, forming the stratum corneum. These cells apparently become 

 changed in their chemical composition, as they are now unaffected by acetic acid. 

 The deepest layer of the rete Malpighii is separated from the papillae by an 

 apparently homogeneous basement membrane, which is most distinctly brought 

 into view in specimens prepared with chloride of gold. This, according to Klein, 

 is merely the deepest portion of the epithelium, and is " made up of the basis of 

 the individual cells, which have undergone a chemical and morphological altera- 

 tion." The black color of the skin in the negro and the tawny color among 

 some of the white races is due to the presence of pigment in the cells of the 

 cuticle. This pigment is more especially distinct in the cells of the deeper layer 

 or rete mucosum, and is similar to that found in the cells of the pigmentary layer 

 of the retina. As the cells approach the surface and desiccate, the color becomes 

 partially lost. 



The derma, corium, or cutis vera, is tough, flexible, and highly elastic, in order 

 to defend the parts beneath frcm violence. 



It varies in thickness, from a quarter of a line to a line and a half, in differ- 

 ent parts of the body. Thus it is very thick in the palms of the hands and soles 

 of the feet ; thicker on the posterior aspect of the body than the front, and on the 

 outer than the inner side of the limbs. In the eyelids, scrotum, and penis it is 

 exceedingly thin and delicate. The skin generally is thicker in the male than in 

 the female, and in the adult than in the child. 



The corium consists of fibrous connective tissue, with a large admixture of 

 elastic fibres and numerous blood-vessels, lymphatics, and nerves. The fibro- 

 areolar tissue forms the framework of the cutis. and is differently arranged in 

 different parts, so that it is usual to describe it as consisting of two layers : the 

 deeper or reticular layer, and the superficial or papillary layer, t nstriped 

 muscular fibres are found in the superficial layers of the corium, wherever hairs 

 are found ; and in the subcutaneous areolar tissue of the scrotum, penis, labia 

 majora of the female, and the nipples. In the latter situation the fibres are 

 arranged in bands, closely reticulated and disposed in superimposed laminae. 



The reticular layer consists of strong interlacing fibrous bands, composed 

 chiefly of the white variety of fibrous tissue, but containing, also, some fibres of 

 the yellow elastic tissue, which vary in amount in different parts, and connective- 

 tissue corpuscles, which are often to be found flattened against the white fibrous 

 tissue-bundles. Toward the attached surface the fasciculi are large and coarse, 

 and the areolse which are left by their interlacement are large, and occupied by 

 adipose tissue and sweat-glands. Below this the elements of the skin become 

 gradually blended with the subcutaneous areolar tissue, which, except in a few 

 situations, contains fat. Toward the free surface the fasciculi are much finer, 

 and their mode of interlacing close and intricate. 



The papillary layer is situated upon the free surface of the reticular layer ; it con- 

 sists of numerous small, highly sensitive, or vascular eminences, the papilla', which 

 rise perpendicularly from its surface. The papillae are conical-shaped eminences, 

 having a round or blunted extremity.occasionally divided into two or more parts and 

 connected by a thin base with the free surface of the corium. Their average length 

 is about j-^ of an inch, and they measure at their base -^i-^ of an inch in diameter. 

 On the genera] surface of the body, more especially in those parts which are endowed 

 with slight sensibility, they are few in number, short, exceedingly minute, and 

 irregularly scattered over the surface ; but in some situations, as upon the palmar 

 surface of the hands and fingers, upon the plantar surface of the feet and toes, 

 and around the nipple, they are long, of large size, closely aggregated together, 

 and arranged in parallel curved lines, forming the elevated ridges seen on the free 

 surface of the epidermis. In these ridges the larger papillae are arranged in a 



