GENERAL CONSIDERATIONS ON THE DIGESTIVE APPARATUS. 327 



A mucous membrane comprises a superficial or epithelial layer and n 

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



Tlir i-j>it}t'-linm is a very thin, inert pellicle, entirely composed of 

 epithi Hal cells united by an almost insignificant quantity of amorphous 

 mattt -r (!>/, ish //(). The cells are flat or polygonul, 

 round or cylindrical, polyhedral, or very irregular 

 in shape. In consequence of these diverse forms, 

 there is pavement (or squamotis), spherical (or 

 spheroidal), and cylindrical or conical (or columnar) 

 'I in in. If the cells are furnished with small 

 filiform appendages, named cibratile cilia, the 

 epithelium is then designated ciliatfd. \\ hen the 



are arranged in a single layer on the surface SQUAMQUS 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 



310 diameters, and exhibits 

 a nucleus with nucleolus in 

 the centre, and seconlary 

 nucleated cells forming the 

 body of the scale. 



upon each other. In stratified epithelium, the 

 shape of the cells is not the same on the surface 

 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 Fig. 144. 



epidermis. It is composed of connective ( or areolar) z 



t is .lie, whose thickness, elasticity, vascularity, and F^T'ft'tifl 

 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, COLUMNAR 

 elastic, and slightly adherent when it lines organs 1, Nucleus of the cell ; 



2, 



Membrane of the cell raised 

 from its contents by the 

 absorption of water. 



Fig. 145. 



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- 

 - they form, under the epithelium, an 

 amorphous surface-layer, the basement (or 

 lini ; tury) membrane. The sub-epithelial face 

 of the corium is scarcely ever smooth, but 

 offers minute prolon gations named tillosities or 

 papilla, which arc very varied in their form COLUMNAR CILIATED Krirmi n M : 

 ami volume, and is more or less marked by """ :il " ""AMKTEBS. 



d, pressions designated follicles. The villi "> Nucleated cells resting on their 

 , .? j ' . j smaller extremities ; 6, Cilia. 



are observed on the deep- seated mucous mem- 



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

 ji ijullae are found towards the natural api-rt UP s. and are rich in nerves ; they 

 more especially the organs of sensibility. Th- t'" 11 ides, lined by ono 

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



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

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

 brane is formed of unstriped lilnvs whoso slow contraction is involuntary. 

 In certain organs those adjoining the natural apertures the unstriped 

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

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

 oesophagus. 



