54 GENERAL ANATOMY OF THE TISSUES. 



by the deeper-seated vessels. They are very easily regenerated 

 when their superficial portions are removed, and in this case 

 they grow chiefly hy the development of new elements in the 

 deeper layers ; even when wholly lost they are readily reproduced. 

 The epidermic tissue takes the following forms : 

 1. Corneous tissue. — This always consists of compact masses 

 of cells, which are soft in the neighbourhood of their vascular 

 basis, but at a greater distance become more or less solid 

 and hard (corneous), and frequently lose their originally 

 vesicular constitution and nucleus, and become the so-called 

 horny scales. The following organs are formed by this 

 tissue : 



a. The Epidermis ; which invests the exterior of the body, 



and is continuous at the great aper- 

 tures of the internal cavities with 

 the epithelium. It consists of two 

 tolerably distinct layers : the mucous 

 layer (rete mucosum), with soft, rounded 

 polygonal cells, which, under certain 

 circumstances, contain colouring mat- 

 ter. This layer applies itself accu- 

 rately to all the inequalities of the 



corium (which nourishes the epidermis), and externally passes 

 into the polygonal scales of the horny layer. 



b. The Nails.— 'These may be regarded as a modification 

 of the epidermis, whose horny layer has attained a still greater 

 density ; and, with its rete mucosum, lies upon a special 

 depressed surface of the cutis, — the bed of the nail; and is 

 partly sunk in a peculiar cleft, — the fold of the nail. 



c. The Hairs. — Filiform epidermic 1 structures, seated upon 

 a vascular papilla, in a peculiar sac, the hair sac, which is a 

 process of the corium, and is lined by a continuation of the 

 epidermis. The structural elements in the region of the 

 papilla are soft and vesicular ; the more distant are meta- 

 morphosed into three kinds of cells — plates, flat fibres, and 

 more or less rounded irregular cells. 



Fig. 12. Plates of the horny layer in man, x 350: 1. without addition, viewed 

 from the surface, one with, a nucleus ; 2, from the side. 



1 [It is to be questioned if the hairs are; truly epidermic structures, vide infra. 

 § Hair.— Ens.] 



