OF THE SEROUS MEMBRANES IN GENERAL. 159 



the two opinions are right. There are cases that favour each 

 of them. Certain tissues that are classed with the cysts, arc 

 evidently pre-existent. In this class we may place the sub- 

 cutaneous wens, which are nothing more than sebaceous folli- 

 cles, considerably enlarged, and not accidental sacs, the cysts 

 of the ovary, which appear to depend upon the extraordinary 

 development of the vesicles of that organ, the cysts of the testi- 

 cular cord of man, or of the labia pudendi of woman, which are 

 the remains of the tunica vaginalis, &c. Another genus of 

 cysts, are, on the contrary, formed consecutively; such are 

 those which follow the effusion of blood which occur in the 

 brain, those which are developed around a foreign body, &c. 

 In other cases it is very difficult to determine the mode and 

 origin of cysts. It is very likely, however, that all true cysts 

 are membranes of a new formation, determined or not by an 

 evident inflammation. The cysts are, besides, subject to all the 

 affections of the serous membranes, to all the varieties of in- 

 flammation, to accidental productions either analogous or mor- 

 bid. They have been found every where, in bones and car- 

 tilages, perhaps, excepted. 



The new cellular membranes, which envelop accidental, 

 analogous, or morbid accidental productions, and foreign bo- 

 dies, are generally confounded with cysts. These envelopes 

 are not like the cysts and the serous membranes, inhalant and 

 exhalant surfaces: they often line the cysts. Their consistence 

 varies : they are also always parts of a new formation. 



Between the cysts or serous vesicles, holding to the cellular 

 tissue by their external surface, and the hydatids, there are 

 insensible transitions, between which it is very difficult to 

 draw a well denned line of demarcation. Thus the little se- 

 rous vesicles, that are so often found in the plexus choroides, 

 those which are sometimes seen at the fringed extremity of 

 the fallopian tubes ; those which I have frequently seen in the 

 vegetation of the nasal and uterine mucous membranes, all evi- 

 dently appear to belong to the cysts. The hydatid or cluster- 

 ed mole appears to me to belong to the same genus, yet a very 

 able physician and naturalist,* refers it to the genus acephalo- 



* See li. Cloquct. Faune des medians, torn. i. Paris 1822. 

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