604 ORGANS OF THE SENSES. 



not unlike a, Pacinian corpuscle, which occupies the principal part of the interior 

 of each papilla, named "tactile corpuscle." The nature of these bodies is obscure. 

 Wagner described them as oval-shaped bodies, made up of superimposed saccular 

 lamina?, presenting some resemblance to a miniature fir cone, and regarded them as 

 directly concerned in the sense of touch. Kolliker considers that the central part 

 of the papillae generally consists of a more homogeneous connective tissue than 

 the outer part, surrounded by a sort of sheath of elastic fibres, and believes that 

 these corpuscles are merely a variety of this structure. The nerve fibres, accord- 

 ing to this observer, run up in a waving course to the corpuscle, not penetrating 

 it, but forming two or three coils round it, and finally join together in loops. 

 These bodies are not found in all the papilla? ; but from their existence in those 

 parts in which the skin is highly sensitive, it is probable that they are specially 

 concerned in the sense of touch, but their absence from the papilla? of other 

 tactile parts shows that they are not essential to this sense. No lymphatics have 

 as yet been discovered in the papilla?. 



The epidermis, cuticle, or scarf-skin, is an epithelial structure, accurately moulded 

 on the papillary layer of the derma. It forms a defensive covering to> the surface 

 of the true skin, and limits the evaporation of watery vapor from its free surface. 

 It varies in thickness in different parts. Where it is exposed to pressure and the 

 influence of the atmosphere, as upon the palms of the hands and soles of the feet, 

 it is thick, hard, and horny in texture ; whilst that which lies in contact with the 

 rest of the body is soft and cellular in structure. The deeper and softest layers 

 have been called the rete mucosum, the term rete being applied, from the deepest 

 layers presenting, when isolated, numerous depressions, or complete apertures, 

 which have been occupied by the projecting papilla?. 



The free surface of the epidermis is marked by a network of linear furrows of 

 variable size, marking out the surface into a number of spaces of polygonal or 

 lozenge-shaped form. Some of these furrows are large, as opposite the flexures 

 of the joints, and correspond to the folds in the derma produced by their move- 

 ments. In other situations, as upon the back of the hand, they are exceedingly 

 fine, and intersect one another at various angles ; upon the palmar surface of the 

 hand and fingers, and upon the sole, these lines are very distinct, and have a 

 curvilinear arrangement, and depend upon the large size and peculiar arrangement 

 of the papilla? upon which the epidermis is placed. The deep surface of the 

 epidermis is accurately moulded upon the papillary layer of the derma, each 

 papilla being invested by its epidermic sheath ; so that when this layer is removed 

 by maceration, it presents a number of pits or depressions corresponding to the 

 elevations of the papilla?, as well as the furrows left in the intervals between them. 

 Fine tubular prolongations from this layer are continued into the ducts of the 

 sudatory and sebaceous glands. In structure, the epidermis consists of flattened 

 cells, agglutinated together, and having a laminated arrangement. In the deeper 

 layers the cells are large, rounded or columnar, and filled with soft opaque contents. 



In the superficial layers the cells are flattened, transparent, dry, and firm, and 

 their contents converted into a kind of horny matter. The difference in the 

 structure of these layers is dependent upon the mode of growth of the epidermis. 

 As the external layers desquamate, from their being constantly subjected to attri- 

 tion, they are reproduced from beneath, successive layers gradually approaching 

 towards the free surface, which, in their turn, die and are cast off. 



These cells are developed in the liquor, sanguinis, which is poured out on the 

 free surface of the derma ; they contain nuclei, and form a thin stratum of closely- 

 aggregated nucleated cells, which cover the entire extent of the papillary layer. 

 The deepest layer of cells, according to Kolliker, are of a columnar form, and are 

 arranged perpendicularly to the free surface of the derma, forming either a single 

 or a double, or even triple, layer ; the lamina? succeeding these are composed of 

 cells of a more rounded form, the contents of which are soft, opaque, granular, and 

 soluble in acetic acid. As these cells successively approach the surface by the 

 development of fresh layers from beneath, they assume a flattened shape from the 



