GENERAL CONSIDERATIONS ON THE DIGESTIVE APPARATUS. 327 



Fig. 143. 



nucleated cells forming the 

 body of the scale. 



A mucous membrane comprises a superficial or epithelial layer and a 

 deep portion which constitutes the derm or chorion (corium). 



The epithelium is a very thin, inert pellicle, entirely composed of 

 epithelial cells united by an almost insignificant quantity of amorphous 

 matter (blastema). The cells are flat or polygonal, 

 round or cylindrical, polyhedral, or very irregular 

 in shape. In consequence of these diverse forms, 

 there is pavement (or squamous), spherical (or 

 spheroidal), and cylindrical or conical (or columnar) 

 epithelium. If the cells are furnished with small 

 filiform appendages, named vibratile cilia, the 

 epithelium is then designated ciliated. When the 

 cells are arranged in a single layer on the surface SQUAM ous EPITHELIUM FROM 

 of the corium, the epithelium is said to be simple / THE MOUTH. 



it is stratified when the cells are arranged in strata The large scale is magnified 

 upon each other. In stratified epithelium, the 310 diameters, and exhibits 

 shape of the cells is not the same on the surface a nucleus wit * nucleolus in 

 and beneath it, and it is named after the form of 

 the superficial layer. 



The mucous derm or corium corresponds to that 

 of the skin, as the epithelium corresponds to the 

 epiderm is. It is composed of connective ( or areolar) 

 tissue, whose thickness, elasticity, vascularity, and 

 sensibility varies with the situation and the func- 

 tion of organs. The corium is thin and almost 

 destitute of elastic fibres when applied to the bony 

 walls of a cavity; on the contrary, it is thick, 

 elastic, and slightly adherent when it lines organs 

 which, like the stomach, oesophagus, and intestines, 

 are capable of increasing or diminishing in capacity. 

 The fasciculi of the connective tissue in the 

 deeper layers of the corium are loosely united, 

 but nearer the surface they lie closer ; some- 

 times they form, under the epithelium, an 

 amorphous surface-layer, the basement (or 

 limitary) membrane. The sub-epithelial face 

 of the corium is scarcely ever smooth, but 

 offers minute prolongations named villositiesoi 

 papillae, which are very varied in their form COLUMNAR CILIATED EPITHELIUM 

 and volume, and is more or less marked by MAGNIFIED 310 DIAMETERS. 

 depressions designated follicles. The villi a > Nucleated cells resting on their 

 are observed on the deep-seated mucous mem- 



COLUMNAR EPITHELIUM. 



Nucleus of the cell; 2, 

 Membrane of the cell raised 

 from its contents by the 

 absorption of watei*. 



Fig. 145. 



smaller extremities ; b, Cilia. 



branes ; they are more particularly the vascular and absorbent organs. The 

 papillae are found towards the natural apertures, and are rich in nerves ; they 

 are more especially the organs of sensibility. The follicles, lined by one 

 or other form of cell, are exclusively organs of secretion. 



b. The second membrane met with in the walls of the hollow organs is of 

 a muscular, and sometimes of a cartilaginous nature. The muscular mem- 

 brane is formed of unstriped fibres whose slow contraction is involuntary. 

 In certain organs those adjoining the natural apertures the unstriped 

 fibres are replaced by striped, which are under the influence of the will, 

 or have the same physiological properties as the smooth fibres, as in the 

 oesophagus. 



