SEROUS AND SYNOVIAL MEMBRANES. 



511 



appello cujus contractus animoe representatur ; 

 et in animalibus brutis, de quorum aiiinm non 

 perincle liquet, eas partes sentientes dico, 

 qiiibus irritatis animal doloris et incommodi 

 signa ostendit ; insensilem contra partem quae 

 usta, scissa, puncta, ad destructionem usque 

 caesa, nullum doloris signum, convulsionem 

 nullam, nullam in totius corporis situ muta- 

 tionem excitat." * 



The sensibility of any part must be judged of 

 by the readiness with which changes in it are 

 perceived by the mind. In general, highly 

 sentient parts, when stimulated, are capable of 

 exciting movements in the muscles of neigh- 

 bouring parts ; thus, stimulation of the sole of 

 the foot excites motions in the whole lower 

 extremity ; the stimulation of any other part 

 of the leg, whilst it might excite movements, 

 would not produce them to the same extent. 

 The difference is due to the greater , sensi- 

 bility of the sole of the foot than of any other 

 part of the integument of the lower extremity, 

 and also to the peculiar connection of its sen- 

 tient nerves with the papillary texture of the 

 skin. 



The anatomical condition necessary for the 

 developement of the greater or less sensibility 

 in an organ or tissue, is the distribution in it 

 of a greater or less number of sensitive nerves. 

 Thus the anatomist can determine the degree 

 to which this property is enjoyed by any 

 tissue or organ by the amount of nervous 

 supply which his research discloses ; and 

 physiological experiments and surgical opera- 

 tions furnish us with abundant evidence in 

 confirmation of the, as it were, a priori sug- 

 gestions of the anatomist. 



The sensibility of tissues is modified by 

 disturbances of their nutrition, and thence in- 

 flammatory affections tend to increased sensi- 

 bility, and will even make parts sensitive 

 which before were but slightly so. Thus the 

 periosteum, which in health is but slightly 

 sensitive, becomes, under the influence of in- 

 flammation, exquisitely sensible. 



It is necessary to add that the word sensi- 

 bility is also used, as applied to nerves, to 

 signify their power of evolving the nervous 

 force. Excitability is a better word for this 

 purpose, and ought to be generally used, 

 to ensure a greater exactness in the applica- 

 tion of physiological terms than has hitherto 

 prevailed. 



(R.B. Todd.) 



SEROUS and SYNOVIAL MEM- 

 BRANES. (Membranes sereuses, Fr.; Serose 

 Halite, Serose Ucberzligc, Wasserhaute, Germ. 

 Membranes synoviales, Fr. ; Synovial-Kapseln t 

 Synovial Saute,Germ.) The names by which 

 these structures are designated seem to have 

 been originally derived from the appearances 

 presented by fluids which are frequently found 

 after death in the so-called cavities formed 

 by their continuous iriterior surface. 



Thus, for instance, rejecting those cases 



* Haller, De Partibus corp human i seuticntibua 

 et inltabilibus. Op. Minora, t. i. p. 407. 



where marked symptoms of disease of these 

 tissues precede death, the structures first 

 named, where they offer any contents at all, 

 present a fluid the colour and composition of 

 which greatly approximate to that of the 

 serum of the blood ; and thence the fluid so 

 found names the tissues yielding it as the 

 " serous " membranes : while the interior 

 of the joints constantly affords a small 

 quantity of a fluid, the viscid consistence of 

 which, resembling that of the white of an 

 egg, gives rise to the application of the name 

 " synovial " membrane (nvr MOV} to the tissue 

 which immediately lines the articulation, and 

 is presumed to yield it. 



But neither do these circumstances, nor 

 that of their membranous form, by which the 

 terms at the head of this article are completed, 

 sufficiently express their most important 

 characteristics. A serous membrane essen- 

 tially consists of an endogenous cell-growth, 

 covering a thin expansion of areolar tissue. 

 The compound structure which results from 

 this arrangement of these two tissues is 

 thrown around the more moveable organs of 

 the body, and also lines the cavities which 

 they fill. By thus affording to these two 

 opposed surfaces uniformity of texture and 

 smoothness of surface, it greatly diminishes 

 their mutual friction ; or, in other words, 

 facilitates their movements upon each other. 



It will, I think, be advantageous to defer 

 for the present all consideration of the pos- 

 sible or probable function of these membranes, 

 as implying by that word an immediate 

 organic operancy in virtue of their intimate 

 structure; and to fix our attention chiefly on 

 their mechanical use in reference to motion. 



In the living man, there are many processes 

 which necessitate changes in the relations to 

 space of the different parts of the body. 

 The actions of locomotion, digestion, circu- 

 lation, and respiration, for instance, all imply 

 some degree of movement in the organs which 

 are their immediate agents, often in the more 

 important parts to which they immediately 

 minister ; and, in many cases the protection 

 of delicate organs appears to be partly ac- 

 complished by an increase of their mobility 

 upon neighbouring structures. The neces- 

 sity of movement thus comes to be more or 

 less participated in by almost all the tissues, 

 organs, and segments of the body ; and as- 

 suming, what is above stated, that it is the 

 most obvious want for which serous mem- 

 branes are destined to provide, we might 

 naturally imagine, either that these structures 

 would pervade as universally as this require- 

 ment, or that those of similar import which 

 should be substituted for them would suffi- 

 ciently approximate in their nature and com- 

 position to be referrible to the same class of 

 tissues : a class, in which the degrees of re- 

 semblance afforded by the different members 

 should somewhat accord with the varying 

 mechanical requirements of those different 

 parts of the body, to the movements of which 

 they were subservient. 



An appeal to facts abundantly confirms 



