466 STRUCTURE OF THE CUTICLE. 



over their convexities ; hence arises the appearance of a network. 

 In the rete mucosum from the hand, these depressions are arranged 

 in a linear series, as are the papillae ; in other situations they are 

 more irregular, but correspond always with the distribution of the 

 papillae. 



The rete mucosum is the freshly secreted layer of cuticle, and 

 gradually hardens as it approaches the surface. It has been shown 

 by Henle to be composed of minute oval vesicular cells, which be- 

 come converted in the hardened cuticle into flattened scales, each 

 containing a central nucleus. The dark pigment of the negro exists 

 in the form of small granules of colouring matter. 



The cuticle (epidermis, scarf-skin) is the horny unorganized 

 lamella which covers and protects the entire surface of the more 

 delicate layers of the skin. In situations exposed to pressure, as 

 the palm of the hand and sole of the foot, it is very thick ; on other 

 parts it forms only a thin layer. The cuticle is marked on the sur- 

 face by a net-work of lines : these are more numerous and larger 

 near to joints, where they form deep wrinkles on account of the 

 inelastic nature of its structure. Their appearance differs in different 

 regions of the body ; but every where depends upon the same cause, 

 the inelasticity of the cuticle. At the entrance to the cavities of the 

 body it is continuous with the epithelium or cuticular covering of 

 the mucous membrane. 



The cuticle, in minute structure, consists of several successions 

 of laminae which are secreted by the cutis ; the last secreted layer 

 being the rete mucosum. The rete mucosum is composed of small 

 round masses or nuclei, connected together by a glutinous fluid 

 containing a number of pigment granules. Each nucleus contains 

 in its interior a minute central point, the nucleus-corpuscule, and 

 around the exterior of the nucleus a vesicle is by degrees produced. 

 The middle laminae of the cuticle are composed of these nucleated 

 vesicles, which are more and more compressed and flattened as they 

 are observed nearer to the surface. In the superficial laminae the 

 vesicles are converted into thin scales, in the centre of which the 

 nucleus with the nucleus-corpuscule is still apparent. The laminae 

 of the cuticle are disposed on the same plane with the surface of 

 the skin in many situations, in others they are placed obliquely so 

 as to project by their free extremities upon the surface ; in the palm 

 of the hand and sole of the foot these layers correspond with the 

 elevations of the papillae, and present an imbricated linear surface. 

 This is particularly seen on the points of the fingers where the rows 

 of papillae have a circular arrangement. The superficial laminae 

 of the cuticle are being continually thrown off by exfoliation or 

 removed by abrasion, to give place to the deep and more newly 

 formed layers. 



Upon the inner surface of the cuticle a number of depressions 

 and linear furrows are seen, corresponding with the projections of 

 the papillae. A number of conical processes are also observed on 



