538 



SEROUS AND SYNOVIAL MEMBRANES. 



a fibrous or fibro-cartilaginous thickening, 

 which is itself the developement of an exsu- 

 dation, is probably the immediate seat of the 

 change ; and a variable quantity of this mor- 

 bid tissue is generally seen around and upon 

 the bony matter. The shape which, under 

 these circumstances, it assumes, is somewhat 

 more regular than that of the preceding 

 variety, it being often flattened and extended 

 in thin plates," the roughly tuberculated sur- 

 face of which is, for the most part, parallel 

 with the surface of the membrane. 



The pleura is the most frequent site of 

 these ossifications, as it is also of the adhe- 

 sions in which they mainly occur : but they 

 are also found in the subarachnoid tissue 

 and pia mater ; and, more rarely, in the peri- 

 toneum and the synovial sheaths of the ten- 

 dons. 



Cysts are often found in these membranes, 

 but their great differences of nature and 

 causes claim a longer notice than can be 

 accorded in this brief sketch. Three chief 

 varieties may be distinguished. One of these 

 is inhabited 'by parasitic animals, as the echi- 

 nococcus. These are usually found in great 

 numbers, and may occur in any of the serous 

 membranes, although the peritoneum is their 

 most frequent locality, probably from its 

 proximity to the intestine by which they are 

 introduced into the body. Sometimes they 

 occupy the cavity of the membrane, and are 

 in contact with its interior by a slightly flat- 

 tened part of their surface; in other instances, 

 they project into the cavity, carrying the 

 membrane before them ; and at least one 

 layer of their wall is formed by lymph de- 

 rived from the neighbouring vessels. Ano.- 

 ther form is not recognised as parasitic, but 

 in the present state of our knowledge might 

 rather be described as a gigantic cell, which 

 often includes a vast progeny of smaller ones* 

 The whitish powder which some of these 

 contain, may frequently be seen to be com- 

 pletely composed of small cells, which are de- 

 void of a nucleus, of uniform size and sphe- 

 rical shape, and exhibit a clear sharp outline. 

 These characters alone would, perhaps, indi- 

 cate their merely cellular nature, as above 

 stated ; but the general appearance of these 

 contained globules is suspiciously like the 

 ova of entozoa. In other cases, the included 

 cell again includes a smaller one, and this yet 

 another, so as to form a series of concentric 

 hollow spheres ; an arrangement which has 

 named them as the pill-box^ hydatid. In their 

 general appearances, they closely resemble 

 the preceding variety. The fluid contents 

 of both are limpid and transparent, and are 

 composed of water, with blood salts (chiefly 

 chloride of sodium), and an exceedingly small 

 quantity of albumen. Yet the effusion of 

 this apparently harmless fluid into the serous 

 cavities gives rise to an inflammation of the 

 greatest violence and fatality. In a third 

 class of cases, the cysts are usually in much 

 fewer numbers than the preceding : they occur 

 for the most part in the neighbourhood of 

 the female reproductive organs ; and this 



their situation, together with their contents, 

 which often consist of teeth, hair, bone, fat, 

 and other products of an abortive develop- 

 ment, sufficiently indicate a relation to the 

 generative process. The fluids which they 

 contain are albuminous, often sufficiently so 

 to possess a glairy consistence. They exist 

 within the cavity of the serous membrane, or 

 in its texture, indifferently ; when developed 

 in or beneath the subserous areolar tissue 

 their gradual enlargement causes them to 

 reach the free surface of the membrane, and 

 then to dilate and extend this tissue before 

 them, until finally the cyst, still covered by 

 the serous layer, hangs freely in the cavity 

 by a more or less elongated peduncle, which 

 is formed by this covering where it becomes 

 continuous with the rest of the serous 

 membrane. 



The subserous areolar tissue has been men- 

 tioned as implicated in most of these diseases ; 

 but other morbid conditions are not wanting, 

 in which it appears to be affected without the 

 essential participation of the remainder of the 

 tissue. Such are the little masses of fat 

 which are occasionally found projecting into 

 the serous cavities ; they are covered by the 

 smooth and apparently healthy membrane, 

 and their form is generally pedunculated, or 

 sometimes ramified and arborescent. The 

 development of this shape corresponds with 

 that of the subserous cysts just mentioned. 

 The fibrinous Pacchionian bodies of the cere- 

 bral meninges have been similarly explained 

 as arising from the pia mater, and gradually 

 invested with a layer of arachnoid which 

 becomes converted into a peduncle, the rupture 

 of which leaves them adhering to the dura 

 mater, or even projecting into the longitudinal 

 sinus. 



Loose cartilages. The cavities of the serous 

 and synovial membranes sometimes* contain 

 morbid products in the shape of certain free 

 or unattached substances, which, from their 

 usual appearance and consistence, are best 

 known as " loose cartilages." The most 

 frequent situation of these bodies is in the 

 knee-joint, and next to this, in the synovial 

 sheaths of the flexors and extensors of the 

 hand or foot j but they are not uncommonly 

 found in the subcutaneous bursae over the 

 patella, trochanter, or acromion. More rarely 

 they are seen in connection with the serous 

 membranes; for instance, in the tunica va- 

 ginalis testis, or in hernial sacs. They may 

 also exist in the diarthrodial species of false 

 joints. 



Their appearances offer great variety in 

 different cases. In some instances, as often 

 happens in the knee-joint, only one, or per- 

 chance two such bodies are present. Here 

 they are of considerable size, attaining the 

 magnitude of a large bean or almond ; their 

 shape is a more or less flattened oval, and 

 their surface is smooth and slippery. Their 

 consistence is firm and elastic, their appear- 

 ance whitish and cartilaginous, their substance 

 uniform and structureless. 



When comparatively recent, or of only a 



