232 OF THE PRIMARY TISSUES OF THE HUMAN BODY. 



when circumstances call for their existence. Thus we find regular synovial 

 capsules formed around " false joints/ ' and newbursae developed between portions 

 of the cutaneous surface exposed to much friction, and the subjacent bones. In 

 all these cases, the cysts appear to originate in an enlargement and fusion of 

 the normal interspaces of areolar tissue, and in a condensation of the tissue itself 

 around the cavities thus formed. Serous membranes, when inflamed, are pecu- 

 liarly prone to throw out plastic exudations, which become organized into " false 

 membranes;" and these frequently constitute " adhesions" connecting their oppo- 

 site surfaces. In this respect, however, the synovial membranes show a marked 

 difference from the more general type ; " adhesive inflammation" being compara- 

 tively rare in them. 1 



228. Mucous Membranes, and their Glandular Appendages. The Mucous 

 membranes, like the serous, derive their name from the attributes of the fluid 

 with which they are moistened; this fluid, however, is not a mere exudation of 

 the watery part of the blood, but is a regular secretion, peculiarly consistent and 

 tenacious in its character, whose purpose is obviously protective. These mem- 

 branes are usually thicker than the serous, and are more or less opaque; they 

 possess, however, comparatively little tenacity; and the reddish color which 

 they exhibit, both during, life and after death, is dependent on the blood con- 

 tained in their copious bloodvessels, and may vary greatly in intensity, according 

 to the degree in which these vessels are congested. There is relatively less 

 fibrous tissue in these membranes than in the serous, a very large part of their 

 substance being formed by bloodvessels and lymphatics; and there are some 

 situations in which it is almost entirely wanting, as in the superficial stratum of 

 the gastro-intestinal mucous membrane, where, immediately beneath the base- 

 ment membrane, we find the vessels spread out amidst a soft granular matter, 

 with a few corpuscles resembling free nuclei and granule-cells. 2 The fibres of 

 the deeper layer are continuous with those of the " submucous" areolar tissue. 

 The presence of a distinct basement membrane cannot be always demonstrated, 

 especially where the membrane presents a simple even surface ; but where the 

 membrane is depressed into follicles (Fig. 23, F, F), or prolonged into villi (v, v), 

 the existence of the basement membrane may usually be clearly made out, 

 though it can seldom be separated from the subjacent tissue. The bloodvessels 

 and lymphatics with which the Mucous membranes are copiously supplied, form 

 a very minute and closely-set plexus which spreads out beneath the basement 

 membrane ; advancing with it into the villi which it covers (Fig. 27), and sur- 

 rounding the follicles which it lines (Fig. 28). The " follicular" arrangement 

 is very common in mucous membranes; the follicles being sometimes isolated 

 from each other, and sometimes clustered so thickly that there is only room for 

 bloodvessels and connective tissue between them. The "villous" character, on 

 the other hand, is for the most part limited to a portion of the gastro-intestinal 

 mucous membrane. The entire surface of the Mucous membranes is covered 

 by an Epithelial layer (e), which not only lies upon their simple flat expansions, 

 but also invests the villi and lines the follicles; the structural characters and 

 physiological uses of this epithelium, however, are so different in different situa- 

 tions, and even in closely-adjacent parts of the same stratum, as to require a 

 more special description ( 230). These cells, instead of forming a comparatively 

 permanent stratum, like the epithelium of serous membranes, are in a state of 

 continual change and renewal; the older layers falling off, whilst new ones are 

 produced from the surface or from the substance of the basement membrane. 

 It is chiefly on the bronchio-pulmonary and gastro-intestinal mucous membranes, 



1 The anatomy and physiology of the serous and Synovial Membranes has been ably 

 treated of by Dr. Brinton, in his Article on that subject in the " Cyclopedia of Anatomy and 

 Physiology," vol. iv. p. 510. 



2 See Dr. Sharpey, in "Quain's Elements of Anatomy," vol. ii. p. 81, Am. Ed. 



