200 SYNOVIAL MEMIJRANES. 



from the serous cavities of recently killed animals coagailates spontaneously, and 

 thus resembles the Ijonph of the Ijonphatic vessels, and, we may add, the liquor 

 sanguinis or plasma of the lilood, the coagulation being, of course, due to the 

 presence of fibrin, or of its two constituents filirinogen and ijara-globultii. Hewson, 

 who regarded the fluid as l^nnj^h, found that the coagulability diminished as the 

 quantity increased. Hewson made his observations on the fluid of the peritoneum, 

 pleura and pericardium, in various animals, viz., luillocks, dogs, geese and 

 rabbits. 



"WTien the fluid gathers in unusual quantitj- as in dropsies, it rarely coagulates 

 spontaneously on being let out ; but will often yield a coagulum on the addition 

 of para-globulin as already stated. From this it may be inferred that fibrinogen 

 is present, but not the para-globulin 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 g-reat 

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

 reconcilable with the mechanical purpose commonlj' ascriljed to these membranes, 

 of lubricating and facilitating the movement of mutually opijosed surfaces. 



"V^lien a serous memljrane is inflamed, it has a great tendency to throw out 

 coagulable lymph (or fibrin) and serum, the two constituents of the blood-jilasma, 

 the fonner chiefly adliering to the inner surface of the membrane, whilst the 

 latter gathers in its cavity. The coagulable lymioh spread over the siirface. in 

 form of a " false membrane," as it is called, or agglutinating the opposed siu-faces 

 of the serous sac and causing adliesion, becomes pervaded by blood-vessels, and in 

 jarocess of time converted into areolar tissue. 



Breaches of continuity in these membranes are readily repaired, and the newly 

 formed portion acquires all the characters of the original tissue. 



SYNOVIAL MEMBRAJSTES. 



Resemblinr^ serous membranes in some respects, the synorial mem- 

 branes are distinguished by the nature of their secretion, for this is a 

 viscid glairy fluid resembling the white of an egg, named si/novia. 



These membranes surround the cavities of joints, and are found in con- 

 nection Avith moving parts in certain other situations ; their secretion 

 being in all cases intended to lessen friction, and thereby facilitate motion. 



The different synovial membranes of the body are referred to three 

 classes, y\z., articular, vesicular, and- vaf/inal. 



1. Articular sjoiovial mem'branes, or Synovial capsules of 

 Joints. — These by their synovial secretion lubricate the cavities of the 

 diarthrodial articulations, that is, those articulations in which the 

 opposed surfaces glide on each other. In these cases the membrane 

 may be readily seen covering internally the surface of the capsular and 

 other ligaments which bound the cavity of the joint, and affording also 

 an investment to the tendons or ligaments which happen to pass through 

 the articular cavity, as in the mstance of the long tendon of the biceps 

 muscle in the shoulder-joint. On approaching the articular cartilages 

 the membrane does not pass over these, but terminates after advancmg 

 but a little way on their surface, witli which it is here firmly adherent. 

 So that, it will be seen, the synovial membranes do not form closed 

 bags lying between the articular cartilages as was supposed by the older 

 anatomists, for the main part of the surfaces of the joints are not 

 covered at all by the membrane, nor even by a layer of epithelioid cells, 

 prolonged from the membrane, as some have supposed. 



In several of the joints, folds of the synovial membrane, often containing more 

 or less fat, pass across the cavity ; these have been called synovial or mucous 

 ligaments. Other processes of the membrane simply project into the cavity at 



