SECRETING CELLS. SEROUS AND SYNOVIAL MEMBRANES. 147 



the outlet, by the continual new growth of cells at the germinal spot.* It is 

 by the continual growth and exuviation of the cells which line the glandular 

 follicles, that the various products of Secretion are separated from the blood ; 

 and it is in cells occupying a similar position, that the Spermatozoa or Repro- 

 ductive particles are developed (Plate I., Fig. 18). In each case, the growth 

 of the cell, and the nature of its product, depend upon its own peculiar 

 vital properties ; and it is a curious fact that the seminal cells, in which the 

 Spermatozoa are formed, are ejected from the gland in the Decapod Crusta- 

 ceous animals, not only before they have burst and set free the Spermatozoa, 

 but even long before the development of the Spermatozoa in their interior is 

 completed, the process being perfected, after the cells have been deposited 

 in the generative passages of the female.t 



7. Of the Compound Membrano-Fibrous Tissues. 



175. Having now considered the Elementary components of the Tissues 

 of the Human body, namely, Membranes, Fibres, and Cells, we proceed 

 to notice certain structures, in which these elements are united in their sim- 

 plest form ; and, in the first place, those termed Serous and Synoviai Mem- 

 branes. AVhen examined with the Microscope, their free surface is found to 

 be covered with a single layer of Pavement-Epithelium, which lies on a con- 

 tinuous sheet of Basement-Membrane. Beneath this last is a layer of con- 

 densed Areolar tissue, which constitutes the chief thickness of the membrane, 

 confers upon it its strength and elasticity ; this gradually passes into that 

 laxer variety, by which the membrane is attached to the parts it lines, and 

 which is commonly known as the subserous tissue. The yellow fibrous 

 element enters largely into the composition of the membrane itself; and its 

 filaments interlace into a beautiful network, which confers upon it equal elas- 

 ticity in every direction. The membrane is traversed by blood-vessels, nerves, 

 and lymphatics, in varying proportions. The Serous and Synoviai mem- 

 branes form, as is well known, closed sacs, which contain a greater or less 

 proportion of fluid. The liquid effused from the Serous membranes is nearly 

 the same with the Serum of the blood; containing as much as 7 or 8 per cent, 

 of albumen and salts; and being distinctly alkaline, from the presence of 

 carbonate or albuminate of soda. There is no reason for regarding it in any 

 other light, than as a simple product of transudation. The fluid contained 

 in the Synoviai capsules, and in the Bursae Mucosae, may be considered as 

 serum with from 6 to 10 per cent, of additional albumen ; it shows an alka- 

 line reaction. :{; The fluid of Dropsy (at least in some forms of this disease) 

 contains in addition urea, and cholesterine suspended in fine plates; also 

 (according to Dr. Kane) stearine and elaine. 



176. The general term Mucous Membrane may be applied to that great 

 system of membranous expansions, which forms the external tegument, or 

 Skin, the lining of the internal cavities whose walls are continuous with it, 

 or Mucous Membrane proper, and the prolongations of this into the secre- 

 ting organs, forming the tubes and follicles of the Glands. These all consist, 

 as Mr. Bowman has justly remarked, "of certain elements, which the 

 Anatomist may detect and discriminate; some of them being essential, others 

 appended or superadded : and the broad characteristic distinctions between 



* Goodsir, in Anatomical and Pathological Observations, Chap. v. 



f Op. Cit. p. 39. 



J This is probably a true secretion, formed by the agency of the epithelium-cells that cover 

 certain delicate highly-vascular fringe-like projections, which hang down into the synovial 

 capsules. 



Cyclopaedia of Anatomy and Physiology, vol. iii. p. 485. 



