SEROUS AND SYNOVIAL MEMBRANES. 



519 



In the following sketch, such details as are 

 more or less common to the synovial mem- 

 branes in general will chiefly be treated of. 

 For a description of their more salient pecu- 

 liarities in the different joints, the reader is 

 referred to the articles headed with the names 

 of the several articulations. 



The epithelium of these structures presents 

 characters which afford some grounds for 

 distinguishing it both from that of the bursal 

 and serous membranes. It forms, for the 

 most part, but one layer, the forms of the 

 constituent cells of which vary to the same 

 extent as those witnessed in the bursae. But 

 the broad, squamous, polygonal epithelia are 

 comparatively rare ; and in by far the larger 

 extent of its surface, the predominant shape 

 is that of a slightly flattened spheroidal, or 

 oval, or somewhat angular cell, such as the 

 majority of those represented in Jig. 399, in 



Fi%. 399. 



a 



Epithelium of Synovia! Membranes. 

 a, free surface seen iu situ; b, separated cells. 

 {Magnified 200 diameters.) 



some of which are seen decussations of two 

 convex outlines, caused by the margin of one 

 cell slightly overlapping that of its neighbour. 

 Acetic acid exerts an unusual effect upon the 

 cell-membrane, swelling up its outline very 

 much before dissolving or rupturing it; an 

 appearance which obtains in the more flat- 

 tened and polygonal epithelia of the serous 

 membranes, but, so far as I have seen, in a 

 much smaller degree. Like those of the 

 bursse, they are firmly attached to the .sub- 

 jacent tissue, and possess little mutual ad- 

 hesion ; though here and there a cluster of 

 two or three more polygonal than usual may 

 be found. Cytoblasts are rare, the cells ap- 

 pearing to be completed by the addition of 

 the outer membrane when yet extremely 

 small, (fig. 399. b.) 



All these peculiarities might perhaps be 

 generalized in the statement, that the cells 

 which cover the general surface of these 

 membranes are in a younger and more active 

 stage of cell-life than those of the bursae. 

 And a slight yet perceptible difference in the 

 same respect has been already indicated as 

 existing between the subcutaneous and sub- 

 tendinous members of this class of structures. 

 Immediately beneath these cells lies a stratum 

 of looser arcolctr tissue, which connects the 

 membrane with the inner aspect of the liga- 

 ments of the joint. It includes little of the 

 yellow fibrous tissue, and its meshes are 

 comparatively few and close : exteriorly, they 

 unite, by a gradation of structure, with the 

 dense white fibrous tissue of which the liga- 

 ments are composed. 



The vessels of the membrane are exceedingly 

 numerous, and its capillaries form a horizontal 

 plexus, which ramifies immediately beneath 

 the epithelium in the areolar tissue just men- 

 tioned. The great vascularity of the tissue 

 has long been known, but the capillaries are 

 not only very numerous, but offer a much 

 more remarkable peculiarity.* They are 

 greatly increased in their length, so as to be 

 everywhere extremely tortuous, and some- 

 times this tortuosity almost amounts to a 

 spiral disposition. On looking at the broad 

 surface of well-injected specimens, an exag- 

 geration of this disposition here and there, 

 gives rise to small patches of tortuous capil- 

 laries ; but the arrangement is clearly a general 

 one, and extends, in some degree, to every in- 

 dividual capillary of the net-work. But though 

 the length of these vessels in a given space is 

 thus greatly augmented, the frequency of their 



Fig. 400. 



Capillaries of the Synoeinl Membrane^ projecting by 

 their convex border over the articular cartilage. 

 From the human finger. 

 a, artery ; v, vein. (Magnified 40 diameters.') 



inosculations does not seem to experience a 

 corresponding increase. Their tortuous form 

 is represented inj%. 400. 



The preceding description of the vascular, 

 fibrous, and areolar constituents of synovia! 

 membrane applies only to the simplest form 

 of that tissue, which consists of a plain flat 

 expanse of membrane. In special joints, as 

 well as in special parts of every joint, each of 

 them experiences modifications deserving of 

 notice. Over the cartilage of the articulation, 

 for instance, all of these cease ; and deferring 

 for the present a consideration of the ana- 

 logous structure which here supplies the 

 place of epithelium, we come to consider the 

 anatomy of the synovial membrane where it 

 reaches the border of articular cartilage. 



The fibrous tissue exterior to the mem- 



* I have here to express great obligations to Mr. 

 Quekett, of the Royal College of Surgeons, since 

 his kindness supplied me both with specimens, and 

 with many further details of this arrangement, till 

 then unknown to me. The joint from which Jig. 400. 

 was sketched, was taken from a hand admirably in- 

 jected by him. 



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