494 



MUCOUS MEMBRANE. 



niotory nerves are almost exclusively found 

 here. The tubules of the sympathetic nerves 

 are chiefly given to the proper mucous mem- 

 branes and to the glands. All these will be 

 considered more at length under other heads, 

 and they are therefore only referred to here. 



Of the areolar tissue. Before describing 

 the remarkable varieties presented by this 

 tissue under different parts of the mucous 

 system, I must advert to its constitution in 

 those situations where its ordinary characters 

 are well marked as in subcutaneous fascia, 

 in muscle, on the exterior of the pharynx, &c. 

 Singular as it may appear, there is no correct 

 account of this structure in any of the works on 

 minute anatomy. It in truth consists of two 

 tissues, distinct from each other, and respec- 

 tively allied to the white and to the yellow 

 fibrous tissues. The white Jibrous element of 

 areolar tissue is chiefly in the form of bands of 

 very unequal thickness, in which are to be 

 seen numerous streaks taking the general direc- 

 tion of the whole, but not parallel to the border, 

 nor continuous from end to end. These streaks 

 more resemble the creases of a longitudinal 

 folding than intervals between separate Hbrillae, 

 for which they have been mistaken. These 

 bands split up without difficulty in the long 

 direction, whence result fibrils of the most va- 

 ried width, the finest being far too minute for 

 measurement, even with the best instruments.* 

 These bands interlace and cross one another in 

 various directions, and their natural course is 

 wavy. They frequently subdivide and join 

 those near them. Besides these bands, com- 

 monly called fasciculi, there are some finer 

 filaments of the utmost tenuity which seem to 

 take an uncertain course among the rest. The 

 yellow fibrous element is everywhere in the 

 form of solitary fibrillae, which correspond in 

 their essential characters with the tissue of that 

 name. They are disposed to curl, and are 

 truly branched at intervals of variable length ; 

 these branches (which usually retain the size of 

 the fibril from which they spring) becoming 

 continuous with others in the neighbourhood. 

 They have higher refractive properties than the 

 white element, and their borders are conse- 

 quently darker. 



It is easy to overlook this twofold compo- 

 sition of areolar tissue in specimens examined 

 in water, but their discrimination is made easy 

 by a trifling artifice. This consists in adding a 

 drop of acetic acid, which instantly swells the 

 white bands, and makes them transparent, but 

 produces no change in the yellow fibrils. These 

 effects of the acid may be watched, if the agent 

 be made to spread gradually over the specimen ; 

 and there can scarcely be conceived a more 

 beautiful example of the aid chemistry will 

 afford anatomy than that presented in the 

 course of this interesting process.-]- The change 



* The fibrillae of true white fibrous tissue are 

 almost precisely similar, and, as I believe, are only 

 produced by the observer himself in opening out 

 his specimen for inspection. 



t In the case of the dartos, this procedure de- 

 tects not only what has just been described, but a 

 third element, hitherto in this situation quite con- 



produced in the white bands is such as to shew 

 very clearly that they are not truly fasciculi, or 

 aggregations of ribrillse. The action of the 

 acid on these two elements is identical with 

 that produced on the two tissues to which I 

 have shewn them to be anatomically allied. 



To these two elements of areolar tissue are to 

 be attributed physical properties similar to those 

 of white and yellow fibrous tissues, and these 

 will vary greatly in different situations, accord- 

 ing to the proportion and mode of arrangement 

 under which the two elements coexist. 



Of the ureolur tissue of glands. There 

 appears to be a very prevalent misconception 

 with regard to the quantity of this tissue 

 found in the interior of the large glands, as the 

 liver and kidney. It is imagined that it pene- 

 trates into every interstice, mingles with the 

 capillary rete, and envelopes the ultimate 

 secreting tubules. It is, however, impossible 

 in the most recent specimen of these organs 

 to discover anything answering to this descrip- 

 tion. All that can usually be detected is a 

 small quantity accompanying the larger vessels 

 in their course within the organ, and forming 

 septa between its coarse subdivisions. And it 

 would be difficult to suppose a purpose which a 

 more abundant supply could subserve. The ca- 

 pillary network and the secreting tubules by their 

 mutual and intricate interlacement sufficiently 

 sustain one arother; no freedom of motion is 

 required between them ; there is no force 

 tending to separate them. 1 am far from 

 saying, however, that the ultimate substance of 

 these glands consists only of simple mucous 

 membrane and bloodvessels. In the inter- 

 stices of these there are probably nerves and 

 lymphatics, of the mode of termination of 

 winch we know nothing, but which seem much 

 fewer than is commonly supposed. There is 

 also more or less of an interstitial amorphous 

 substance, hereafter to be described. 



In these glands and in the substance of 

 many compound mucous membranes there are 

 to be seen here and there small bodies not 

 unlike cellular tissue in an early stage of its 

 development. They have a bulging nucleus 

 from which they taper to the extremities; and 

 they are much longer and slenderer than the 

 prismatic epithelium. With their nature and 

 use I am at present quite unacquainted. 



The lungs seem mainly to owe their extraordi- 

 nary elasticity to the yellow fibrous element of 

 their submucous areolar tissue. This is spread 

 in great abundance under the whole surface, 

 and much predominates over the white. In the 

 trachea and bronchia it is besides largely deve- 

 loped in longitudinal bands visible through the 

 mucous membrane. In the whole of tins re- 

 gion its fibrils take a general longitudinal direc- 

 tion, but branch and inosculate at very frequent 

 intervals, enclosing areola; of small dimensions. 

 But this element does not cease with the tubes; 

 it is prolonged in the form of branching, arching 

 bands over the basement membrane of the air- 

 cells, which it renders elastic and fii mly supports. 



founded with areolar tissue. This is non-striated 

 muscle, at once known by its bein^ loaded wiih 

 corpuscles, or persistent cell-nuclei. See MUSCLE. 



