SEROUS AND SYNOVIAL MEMBRANES. 



525 



plexiform arrangement, which occupies, for the 

 most part, a plane parallel to the surface of 

 the membrane. Lymphatics in considerable 

 numbers exist in the same situation. 



Nerves. Little is known of the manner in 

 which these tissues generally are supplied with 

 nerves. In the case of most of them, anatomy 

 sufficiently shows that the amount of nervous 

 tissue which they receive for distribution is 

 but small ; and at present, even the aid of the 

 microscope does not seem materially to affect 

 this statement. The observations of Pur- 

 kinje*, and more recently of Volkmann-j- and 

 Raineyf, however, agree in verifying the exist- 

 ence of a large number of nerves in connec- 

 tion with the cerebral and spinal arachnoid. 

 They appear not to communicate with the 

 roots of the spinal nerves, but to pertain ex- 

 clusively to the sympathetic system ; and they 

 branch and form plexuses in the areolar tissue 

 beneath the arachnoid. But how far they are 

 related to this membrane, or the serous mem- 

 branes generally, or whether they belong more 

 to the pia mater and other subjacent textures, 

 seems at present incompletely determined, 

 and is a question which will require an ex- 

 tended comparison with the other serous 

 tissues. 



The very painful nature of the diseases of 

 these membranes is singularly contrasted with 

 the slight amount of sensation of which they 

 are capable in a state of health. It is pro- 

 bable that, as in the bowels, bones, and some 

 other tissues, this contrast mainly depends on 

 the minutiae of the anatomical arrangements 

 ef the nerves relatively to the tissue. In the 

 serous membrane, this may perhaps receive 

 some explanation when we call to mind that 

 almost every morbid change to which they are 

 liable has the immediate effect of converting 

 a smooth, moist, and plane surface into one 

 the nature and disposition of which implies a 

 vast amount of friction, and the abnormal 

 character of which draws this important dis- 

 tinction between it and other normal surfaces 

 which rub with far more force : viz. that no 

 provision has been made to guard against it. 

 And if the arrangement of the nerves, what- 

 ever be its other features, allots to them as 

 great a proximity to the surface as is granted 

 to the vessels, it seems tolerably obvious, 

 that any such friction would, in reality, 

 amount to a serious injury of these delicate 

 nervous filaments, and would be quite suffi- 

 cient to account for the intense pain expe- 

 rienced. 



In addition to the preceding tissues in- 

 cluded in the ordinary enumeration of the se- 

 rous membranes, there are other parts of the 

 body which present structures so closely re- 

 sembling these, as to render it perhaps doubt- 

 ful whether this title can justifiably be with- 

 held from them. The ventricles of the brain 

 are lined by a membrane which exhibits the 



* Miiller's Archiv. 1845. 



f Wagner's Handworterbuch der Physiologic, 

 artikel " Nervenphysiologie." 



% Medico-Chirurgieal Transactions for the year 

 1845. 



characteristic smooth and shining appearance 

 of the serous tissues ; the posterior surface 

 of the cornea is occupied by a similar layer ; 

 and, according to Henle, there are consider- 

 able grounds for conjecturing the existence of 

 some such structure on the inner surface of 

 the membranous labyrinth and semicircular 

 canals. But without here entering into the 

 question of a possible transition of mucous 

 into serous membranes being represented by 

 these tissues, it will be sufficient to point out 

 that while the ventricular and corneal mem- 

 branes present a stratum of epithelial cells 

 analogous to those described above, they are 

 almost or entirely deficient in the important 

 element of areolar tissue, and that this 

 constitutes a difference according to which 

 the line of distinction is drawn, excluding 

 them from the serous membranes. The epi- 

 thelium which lines the general surface of the 

 cerebral ventricles consists of flattened poly- 

 gonal cells which are covered with cilise ; but 

 where it passes over the choroid plexus, it 

 varies so considerably from this description 

 as to merit a special notice. 



The choroid plexus occupies the descending 

 cornua of the lateral ventricles, and forms the 

 margins of the velum interpositum, the inti- 

 mate structure of which it resembles in many 

 respects. It consists chiefly of an interlace- 

 ment of capillaries and capillary arteries. The 

 former are of large size and great tortuosity ; 

 and, in this last respect, they are similar to 

 those of the synovial membrane already de- 

 scribed. A little areolar tissue surrounds and 

 supports the vessels, and a stratum of cells 

 covers the surface of the plexus. Besides 

 these structures, a large number of nerves 

 have been described by Mr. Rainey as rami- 

 fying beneath the cells, but Purkinje and 

 other observers deny the existence of nerves 

 in this situation. Concerning the shapes of 

 the cells which cover the plexus, similar dif- 

 ferences of opinion and description obtain ; 

 Henle *,Valen tin f, and other high authorities 

 speak of them as being in general polygonal, 

 but somewhat flattened and curved where 

 they cover the fringes of the plexus ; while, on 

 the other hand, Mr. Rainey attributes to them 

 a spherical shape and faintly granular con- 

 tents. The following are their appearances 

 as noted by the writer of this article. 



At the margins of the fringes are seen 

 many long and tortuous capillaries, the gene- 

 ral course of which is parallel to the border 

 of the plexus, and interrupted by few anasto- 

 moses. No basement membrane can be de- 

 tected interposed between these vessels and 

 the cells. The cells themselves are of a sphe- 

 rical shape, and of the very large size repre- 

 sented in the sketch (fig. 404.), many of them 

 being one five-hundredth of an inch in diameter, 

 a magnitude rarely paralleled by any cells 

 but those of the adipose tissue : they contain 

 a tolerably large nucleus in contact with their 

 inner surface. Where exposed to the slightest 

 pressure, they take a polygonal shape, but I 



* Allgemeine Anatomie, S. 228. 



\ Wagner's Handworterbuch, artikel " Gewebe." 



