. The comparative anatomy of the domesticated animals. Veterinary anatomy. 796 THE APPABATIS OF THE SENSES. Fi2. 369. Structure.âThe epidermis comprises two layers, whicli are not very distinct from each other in the Horse. The deep layer, or refe mucosum. is composed of soft, nucleated, pigmentary cells, which are round on the surface of the derma, and polyhedric elsewhere. The superficial, or Iwrny layer, is constituted by hard, horny, flattened cells, which still contain some pigment- granules, and are insensibly confounded with those of the rete mucosum. (The theory of growth of the epider
. The comparative anatomy of the domesticated animals. Veterinary anatomy. 796 THE APPABATIS OF THE SENSES. Fi2. 369. Structure.âThe epidermis comprises two layers, whicli are not very distinct from each other in the Horse. The deep layer, or refe mucosum. is composed of soft, nucleated, pigmentary cells, which are round on the surface of the derma, and polyhedric elsewhere. The superficial, or Iwrny layer, is constituted by hard, horny, flattened cells, which still contain some pigment- granules, and are insensibly confounded with those of the rete mucosum. (The theory of growth of the epidermis is believed to be as follows :âa layer of plastic lymph is thrown out on the surface of the derma, and is converted into granules, which are termed cell-germs, or cytoblasts. These imbibe serum from the lymph and adjacent tissues, so that the outermost covering of the cytoblast is gradually distended ; the latter becomes a cell, and its solid portion, which always remains adherent to some point of the inner surface of the cell membrane, forms the nucleus of the cell. Within this nucleus one or more nuclei are developed; these are named nucleoli. The process of imbibition continuing, the cell becomes more or less spherical; so that, after a certain time, the papillary layer of the derma is covered by a thin stratum of spherical cells pressed closely together, and corresponding with every irregularity of the papillae. New cells being continually produced before the formation of the others has been quite completed, these are removed in layers further and further from the surface of the derma, and becoming subjected to the influence of physical laws, their fluid contents evaporate: they collapse, flatten, and gradually assume an elliptical shape; then they are a mass of completely flat cells, with an included nucleolated nucleus, and finally become a thin mem- branous scale, in which the nucleus is scarcely appa- rent). In Solipeds and other animals, the epidermis is generall
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