228 



MANUAL OF HISTOLOGY. 



Fig. 221. Diagram of a mucous 

 membrane clothed with col- 

 umnar cells, a, the cells; 

 6, 6, the intermediate sub- 

 stance between their lower 

 extremities; c, transparent 

 layer or basement membrane ; 

 d, mucous membrane tissue 

 formed of fibrous connective- 

 substance. 



136. 



7. Whilst the serous membranes are poor in blood-vessels, as we have 



just seen, we have to deal, in considering the 

 cutis (fig. 219), with a structure very different 

 from them in this respect. The 1 latter consists of 

 a very vascular tissue, made up of densely 

 interwoven fibrillated bundles of connective- 

 tissue, accompanied by very numerous elastic 

 fibres. It possesses connective-tissue and emi- 

 grated lymphoid corpuscles also. In the papillae 

 alone (fig. 220) and on the surface does its 

 fibrous character become less strongly marked, 

 giving place to a more homogeneous appear- 

 ance on account of the interweaving of the 

 filaments becoming so intimate as to get rid of 

 all interstices (Rollett). Here, then, we may accept the presence of a 

 structureless limiting layer, the so-called intermediate membrane of 

 Henle, or basement membrane of Todd and Bowman (comp. p. 84). 

 The cutis is covered by the strongest bed of epithelium in the body, 

 namely, by the epidermis. Further, it is rich in nerves, contains many 

 small bundles of smooth muscular fibres, possesses lymphatic canals, 

 and is traversed by the hairs and their follicles as well as the ducts of 

 numerous glands. Below it is continuous with the soft fatty subcutaneous 

 connective-tissue (fig. 219, h). 



8. The tissue of the mucous membranes, which is also very vascular, 

 has a similar structure to that of the corium, if it do not consist, as in, 

 the small intestine especially, of reticular connective-substance containing 

 lymphoid cells. We have already considered (at 88, 91, 93) the various 

 kinds of epithelium which may be found clothing it, all having their 

 origin from the lower or intestinal glandular plate of the embryo. The 

 true mucous membrane (fig. 221, d) consists of interlacing bundles of con- 

 nective-tissue of softer constitution and looser texture, however, than those 



in the cutis. The proportion of elastic 

 matter here is liable to variation, but 

 is smaller than in the skin. Super- 

 ficially, as well as in the various 

 prominences of the tissue, e.g., in the 

 villi, papillae, and folds, the fibrous 

 character becomes fainter, so that we 

 not unfrequently have here, as in the 

 cutis, a transparent layer (c). But the 

 mucous membrane tissue in different 

 organs varies to a certain extent. In 

 those parts, for instance, where it is 

 less abundant, owing to the presence of a large number of glands lying 

 close together, it usually appears as a more or less streaky or slightly 

 fibrillated substance containing nuclei (fig. 222). On its deep aspect 

 it is continuous with the submucous connective-tissue, which is remark- 

 able in many parts, and more especially in the digestive tract, for 

 .s ^strong texture and white appearance, and which constitutes the 

 tunica nervea of older anatomists. The mucous membranes, which are in 

 general very vascular, possess a varying number of lymphatics and nerves. 



Fig. 222. Transverse section through the mu- 

 cous membrane of a rabbit's stomach. CT, 

 tissue of the mucous membrane ; 6, sections 

 of empty vessels ; c, the latter injected ; d 

 spaces for tiie peptic glands.. 



