STRUCTURE OP MUCOUS MEMBRANES. 



407 



or retiform tissue. It is usually bounded next to the epithelium by a basement 

 membrane (fig. 465, bm), and next to the submucous tissue by a thin layer of non- 

 striated muscular tissue termed the muscularis mucosce, (mm). 



The basement membrane is not everywhere demonstrable, but where it is well 

 marked it appears in section as a thin line immediately underlying the epithelium. 

 Viewed on the flat and with the superjacent epithelium removed, the membrane in 

 question seems at first sight homogeneous ; but treatment with nitrate of silver 

 brings to view the outlines of the flattened cells of which it is in reality composed. 



Fig. 465. SECTION OF MUCOUS MEMBRANE FROM 



THK STOMACH OF THE KANOAROO. MAGNI- 

 FIED ABOUT 260 DIAMETERS. (E. A. S. ) 



e, columnar epithelium of the surface, con- 

 tinued into the neck, ?t, of the simple tubular 

 glands, gl ; but becoming at first cubical, and 

 then polyhedral towards the base, b, of the 

 glands ; It, lymphoid tissue ; bm, basement 

 membrane, bounding the corium superficially ; 

 mm, muscularis mucosas, bounding the mucous 

 membrane at its attached surface, and sending 

 small bundles of plain muscular tissue between 

 the glands. The commencement of a lymphatic 

 vessel is shown between two of the glands. 



It is not always a complete membrane, 

 for in some parts the cells composing 

 it, instead of adhering closely by their 

 edges, intercommunicate by branching 

 processes so as to form a network 

 instead of a continuous membrane. 

 The basement membrane follows all 

 the eminences and depressions of the 

 surface of the mucous membrane, dip- 

 ping down to take part in the forma- 

 tion of the wall of the glands, and 

 passing over the raised villi and other 

 prominences. 



The muscularis mucosce forms the deepest part of a mucous membrane, but it is 

 not everywhere present. It is, best developed in the mucous membrane of the 

 alimentary canal, in some parts of which it may consist of two layers, in the one of 

 which the fibres are longitudinal, in the other circular in direction. From its inner 

 surface muscular bundles bend inwards into the thickness of the mucous membrane, 

 passing between the glands contained within it, and even into its prominences, so 

 as in many cases to reach and become attached to the basement-membrane covering 

 them (as in the villi of the small intestine). The muscularis mucosas is a part 

 therefore of the mucous membrane, and is not to be confounded with the muscular 

 coat proper, which forms a separate layer in most of the hollow viscera. 



The connective tissue layer or corium proper varies much in structure in different 

 parts. In some situations, as in the gullet, bladder, and vagina, the filamentous 

 connective tissue is abundant, and extends throughout its whole thickness, forming 

 a continuous and tolerably compact web, and rendering the mucous membrane of 

 those parts comparatively stout and tough. In the stomach and intestines, on the 

 other hand, where the membrane is pervaded by tubular glands, the tissue between 

 these is chiefly retiform or lymphoid tissue (fig. 465, It) with but few white and 

 elastic fibres, and hence in these situations the membrane, although thicker, is far 

 less firm and tough than in parts where much of the white connective tissue is 



