516 



SEROUS AND SYNOVIAL MEMBRANES. 



it is almost impossible to observe both these 

 different layers in situ, from the transparency 

 and flatness of the objects just named causing 

 them to be effectually shrouded and lost in 

 the outline of the granular polygonal layer ; 

 but, from various reasons, 1 have little doubt 

 that the preceding description may be re- 

 garded as tolerably correct. It is especially 

 countenanced by these facts, that in looking 

 directly upon the free surface, 1 have never 

 seen cells referrible to either of the two ex- 

 tremes, but always such as from their shape, 

 their size, and the mutual distances of their 

 nuclei, would be included in the varieties 

 (c, d,f) ; while, nevertheless, a careful tearing 

 up of the same specimen often afforded the 

 cytoblasts and scales. The latter were in 

 much greater quantity than the former, but 

 whether they existed over the whole surface 

 of the bursa, or on particular parts only, I am 

 unprepared to state. And whether the cyto- 

 blasts chiefly underlie the oval or the poly- 

 gonal forms, is a question equally impossible 

 to answer satisfactorily, yet by no means so 

 insignificant an inquiry as it may seem at first 

 sight. On the whole, their usual appearance 

 in conjunction with the younger forms, and 

 their comparative absence from the polygonal- 

 celled serous membranes, somewhat tend to 

 associate them more with the oval than with 

 the polygonal epithelia. 



The subtendinous bursts. It frequently 

 happens that, where tendons in passing to 

 their insertion lie upon a bone, the action of 

 the muscle with which they are continuous 

 gives rise to considerable friction of the two 

 surfaces against each other: and, in some 

 cases, the projecting surface of the bone is 

 even made the pulley by means of which the 

 direction of the muscle's action is altered, 

 through a similar change in the course of the 

 tendon ; a condition which necessarily implies 

 a yet greater amount of resistance and fric- 

 tion. In these circumstances, bursae are 

 found interposed between the osseous and 

 tendinous surfaces. These bursse have* 

 hitherto been regarded as in all respects 

 similar to the subcutaneous sacs just de- 

 scribed, and the possession of an epithelial 

 lining has been denied them equally with these. 

 But while they apparently present the same 

 form, that of a shut sac, continuous with itself 

 in every part, and are, in the majority of in- 

 stances, indistinguishable from them by the 

 naked eye, they are yet separated from them 

 by important differences. They present, it 

 is true, a cell-growth analogous to that de- 

 scribed in the preceding structures ; but they 



* Since writing the above, I have been informed 

 that a description of these structures, somewhat re- 

 sembling that given by the writer, has appeared in 

 a provincial German periodical of a few months' 

 earlier date. I have been unable to meet with it 

 however. So also, the account which I have given 

 of Synovial Membranes must not be understood as 

 claiming any priority. I believe that priority (and 

 probably something more) belongs to Mr. Rainey ; 

 a report of whose paper has appeared in the " Pro- 

 ceedings of the Royal Society," a publication which 

 I have found difficult of access. 



differ from these in the extent of surfac eon 

 which that growth obtains, in the nature of 

 the tissues which are substituted where it is 

 absent, and, in a lesser degree, in the general 

 characters of the membrane where it is pre- 

 sent : the general effect of these differences 

 being greatly to liken the anatomy of these 

 structures to that of the joints. 



On laying open one of the least complicated 

 of these bursae, such as they are generally 

 seen in the dog and cat, we gain entrance to 

 a simple cavity, which everywhere possesses 

 a smooth and shining interior. Above is the 

 tendon, below the periosteum of the bone ; on 

 either side, a delicate continuous membrane 

 separates it from the neighbouring areolar 

 tissue. It might be expected that this mem- 

 brane covered the neighbouring opposed sur- 

 faces of tendon and periosteum ; and, indeed, 

 the description usually given by authors affirms 

 the existence of such a covering, to which it 

 attributes the smoothness of their surfaces. 

 But this is not the case : a careful examination 

 of these structures with the microscope dis- 

 tinctly shows that their surfaces of friction 

 are quite devoid of this membrane, and have 

 assumed more or less of the structure of 

 cartilage. 



The membrane, then, may be described as 

 preserving the continuity of the inner surface 

 of the bursae in the interval between the two 

 rubbing surfaces. It is attached to the ten- 

 don and periosteum by a mingling of its 

 areolar tissue with these structures. Like 

 its neighbouring areolar tissue, it is extremely 

 elastic and delicate ; so that its tenuity often 

 equals that of the serous membranes. It is 

 plentifully supplied with blood-vessels ; and, 

 generally, there is a considerable amount or 

 adipose tissue on its attached surface, the 

 capillaries of which are arranged in J:he same 

 manner as those in the bursae previously men- 

 tioned, or those which supply the fat cells of 

 the so-called " Haversian glands " in the 

 joints : viz. the same capillary plexus, which 

 immediately underlies the epithelium, gives 

 off occasional loops to surround the adipose 

 vesicles. The epithelium itself resembles that 

 of the subcutaneous bursae in the intimacy of 

 its adhesion to the subjacent tissue, as well 

 as in the comparatively slight connection 

 which subsists between the cells themselves : 

 but it appears to differ from it in the greater 

 quantity of the oval cells and cytoblasts, of 

 the former especially : and in the immediate 

 neighbourhood of the fat vesicles this shape 

 seems to predominate to the comparative ex- 

 elusion of polygonal forms. 



In the human subject, the surface of bone 

 on which the tendon plays often presents a 

 covering of what has all the appearances 

 of fibrous tissue mingled with cartilage, or 

 " fibro-cartilage ;" and even in smaller animals 

 (as the cat), in whom the tissue offers no 

 visible difference from the neighbouring peri- 

 osteum, its intimate structure exhibits a simi- 

 lar transition. The bursa beneath the tendon 

 of the obturator internus, where this turns 

 over the border of the ischiurn in its pro- 



