SYNOVIAL MEMBRANES. cxciii 



cavity by cognisable apertures, as already stated. Fine nervous fibres, 

 with nerve-cells in some places, have been described by several auatoniists, 

 in or immediately beneath the serous membranes of various regions ; never- 

 theless it would seem, that when in a healthy condition these membranes 

 possess little or no sensibility ; they are altogether devoid of vital contractility. 



Fluid. The internal surface of serous cavities is moistened and lubricated with a 

 transparent and neaily colourless fluid, which in health exists only in a very small 

 quantity. This fluid, which is doubtless derived from the blood-vessels of the mem- 

 brane, has been commonly represented as similar in constitution to the serum of the 

 blood. But it was long since remarked by Hewson (and a similar opinion seems to 

 have been held by Haller and Monro), that the fluid obtained from the serous cavities 

 of recently killed animals coagulates spontaneously, and thus resembles the lymph of 

 the lymphatic vessels, and, we may add, the liquor sanguinis or plasma of the blood, 

 the coagulation being, of course, due to the presence of fibrin, or of its two con- 

 stituents fibrinogen and globulin. Hewson, who regarded the fluid as lymph, 

 found that the coagulability diminished as the quantity increased. In confirmation of 

 Hewson's statement, I may mention that I have always found the fluid obtained from 

 the peritoneal cavity of rabbits to coagulate spontaneously in a greater or less degree. 

 Hewson made his observations on the fluid of the peritoneum, pleura, and pericardium, 

 in various animals, viz., bullocks, dogs, geese and rabbits.* 



"When the fluid gathers in unusual quantity as in dropsies, it rarely coagulates spon- 

 taneously on being let out ; but will often yield a coagulum on the addition of globulin 

 as already stated (page xxxviii.). From this it may be inferred that fibrinogen is 

 present, but not the globulin (fibrino-plastin) requisite to generate fibrin. 



The identity in character of the fluid of serous cavities and the lymph-plasma is, it 

 need scarcely be remarked, in keeping with the notion of their being great lymph- 

 spaces in open connection with lymphatic vessels. But this view is quite reconcilable 

 with the mechanical purpose commonly ascribed to these membranes, of lubricating 

 and facilitating the movement of mutually opposed surfaces. 



When a serous membrane is inflamed, it has a great tendency to throw out coagu- 

 lable lymph (or fibrin) and serum, the two constituents of the blood-plasma, the 

 former chiefly adhering to the inner surface of the membrane, whilst the latter 

 gathers in its cavity. The coagulable lymph spread over the surface, in form of a 

 " false membrane," as it is called, or agglutinating the opposed surfaces of the serous 

 sac and causing adhesion, becomes pervaded by blood-vessels, and in process of time 

 converted into areolar tissue. 



Breaches of continuity in these membranes are readily repaired, and the new-formed 

 portion acquires all the characters of the original tissue. 



SYNOVIAL MEMBRANES. 



Resembling serous membranes in general form and structure, the synovial 

 membranes are distinguished by the nature of the secretion which lubricates 

 their surface, for this is a viscid glairy fluid resembling the white of an egg, 

 and thence named synovia. 



These membranes line the cavities of joints, and are interposed between 

 moving parts in certain other situations ; being in all cases intended to 

 lessen friction, and thereby facilitate motion. They are composed of a scaly 

 epithelium, which may consist of several strata, and a layer of dense 

 areolar tissue pervaded by vessels and attached by tissue of the same kind 

 to the parts beneath. 



The different synovial membranes of the body are referred to three classes, 

 viz., articular, vesicular, and vacjinal. 



1. Articular synovial membranes, or Synovial capsules of joints. These 



* See Hewson's Works, published by the SydenLam Society, p. 157, with some 

 important remarks in notes xviii. and Ixviii., by the editor, Mr. Grulliver. 



