SEROUS AND SYNOVIAL MEMBRANES. 



exerted its ordinary effect ; defining their 

 outline, and deepening their colour. But 

 although the existence of a stratum of nuclei 

 was sufficiently distinct, the contour of the 

 cells themselves he does not seem to have 

 determined. 



The resemblance of these bursae to the 

 membranes which form the especial subject of 

 this article is thus rendered so complete as to 

 deserve a brief notice of their structure in this 

 place ; and the more so, perhaps, that the 

 writer is enabled to add a few details which 

 place this similarity in a still more striking 

 light. 



The subcutaneous bursts are the simplest 

 form of these structures, and are very nume- 

 rous in the human subject, but seem much less 

 frequent in other animals. 



The arcolar tissue which immediately in- 

 vests these sacs is, for the most part, very lax, 

 and containsan unusual quantity of the yellow 

 fibrous element, the fibres of which are here 

 of large size. 



On removing this from the outer surface of 

 the bursa, it is seen to be composed of a more 

 compact and whiter tissue, which is tough 

 and much less extensible than the looser tex- 

 ture which surrounds it. The microscope 

 shows this to consist of the white and yellow 

 fibrous tissues. The latter is generally in 

 much less considerable proportion than in 

 the ordinary areolar tissue, while at the same 

 time its constituent fibres are of a smaller size : 

 they possess their ordinary arrangement, and 

 branch and unite sparingly with each other. 



The white fibrous element is disposed in 

 wavy bands of varying size. These take a 

 course parallel with the surface of the bursa, 

 and, apparently, with few interstices or reti- 

 culations ; thus forming a dense laminated 

 structure, which cannot be broken up without 

 much difficulty. In this structure, at a little 

 distance from the interior, are arranged the 

 blood-vessels, the capillary meshes of which 

 are of tolerably large size, and generally take 

 a more or less quadrangular shape. It is by 

 no means unusual to find one, two, or more 

 fat cells lying comparatively isolated in this 

 mass of tissue, with a loop or curve of capil- 

 lary thrown around them in the ordinary 

 imnner. Of the nerves of these membranes 

 I am not qualified to speak. As the white 

 fibrous tissue approaches the internal or free 

 surface which limits the cavity, the bands ap- 

 pear somewhat to differ from this descrip- 

 tion, and become more refractile, acquiring a 

 yellowish colour, and seeming more solid. 



The interior of the bursa forms a cavity 

 which is very rarely a solitary and regular 

 one, being almost always complicated by the 

 possession of membranes and threads, which 

 run across its interior, and thus shut off in- 

 complete secondary cavities. The number 

 and situation of these is quite irregular in dif- 

 ferent subjects ; and, of the two complications, 

 the first is the most common, giving rise to the 

 production of folds, which project into the 

 general cavity in a manner which maybe com- 

 pared to those processes of dura mater, which 



form the tentorium and falx cerebri. The 

 surface itself is hard and smooth, and the 

 blade of a knife removes little or nothing from 

 it by scraping with any ordinary force. 



It deserves to be stated that in examining 

 different specimens differences are seen, both 

 in the amount of the yellow or elastic tissue, 

 and in the degree of condensation of the 

 white element, which ought to be called con- 

 siderable, i.e. that they seem to range, from 

 tough, inextensible, white sacs, of compara- 

 tively simple form and composed of little but 

 white fibrous tissue, to a highly elastic mem- 

 brane, containing a tolerable quantity of the 

 yellow fibrous tissue, and a cavity much com- 

 plicated by numerous threads and processes. 

 How far these diversities are associated with 

 differences of age or habit, it is impossible to 

 state. 



The whole of this internal surface is covered 

 by a cell-growth, but the exact shape and ar- 

 rangement of the constituent particles are 

 rendered difficult of observation by one or two 

 physical peculiarities not devoid of interest. 

 On examining the free aspect of a thin hori- 

 zontal section, made just below the surface, 

 the dark mass of fibrous tissue upon which 

 the cells are placed, obscured and intersected 

 by the numerous lines which mark its fibres, 

 very seldom allows more than a layer of nu- 

 clei to be observed. And the application of 

 acetic acid, which swells up this tissue, and 

 renders it transparent, at the same time dis- 

 solves the cell-wall, and leaves the dark nu- 

 cleus alone occupying its place. On the 

 other hand, scraping the surface, instead of 

 obtaining a layer of cells, mutually adherent 

 by the adapted sides of their polygonal mar- 

 gin, and easily separated from the subjacent 

 tissue, as is the case with the serous mem- 

 branes, instead of this, little or nothing is 

 stripped off, save a few scattered cells with 

 much debris and many oil-globules. If 

 greater violence be used, a portion of the sub- 

 jacent structure is torn off, and offers the 

 same optical difficulties as the thin section 

 alluded to. 



The careful and repeated examination of 

 different portions and fragments, both with 

 and without the application of dilute acetic 

 acid, leads to the following results. 



I have been unable to verify the existence 

 of a basement membrane, although, on analo- 

 gical grounds, it might perhaps have been ex- 

 pected that such a structure was present. On 

 getting a favourable view of a vertical section, 

 the surface immediately beneath the epithe- 

 lium appears to be smooth and defined ; but 

 there is nothing which resembles the other 

 surface of a membrane intervening between 

 the cell-growth and the fibrous tissue. The 

 latter appears to be immediately subjacent to 

 the cells, and is continued outwards without 

 any interruption to the surrounding areolar 

 tissue, in which course it is subject to the 

 modifications already described. 



In one instance only many elongated nu- 

 clei were observed, which were of extreme 

 delicacy, and were seated upon or in a mem- 



