SECT. 26.] CONNECTIVE TISSUE. 57 



d. The serous membranes. These are formed of connective tissue, 

 which contains much fine clastic tissue, and consists of bundles 

 interwoven in various ways, or actually anastomosing together in 

 a reticular manner, but which may also, in some cases, present a 

 more homogeneous character, especially at the surface of the 

 membrane. The serous membranes, which are always destitute of 

 glands, and have, on the whole, but few vessels and nerves, line 

 the cavities containing the viscera, and are rendered smooth and 

 shining upon the inner surface by an epithelial covering. They 

 do not necessarily form shut sacs, as was formerly believed, but 

 may have openings (abdominal opening of the Fallopian tubes), or 

 be absent altogether over certain parts of the surface of the cavity, 

 as upon articular cartilages. In other cases, their basis of connective 

 tissue may be wanting, and then the epithelium lies on another 

 structure, as in the case of the so-called outer lamina of the cere- 

 bral arachnoid. To these membranes belong : I. the proper serous 

 membranes, as the arachnoid, the pleura, the pericardium, peri- 

 toneum, and the tunica vaginalis, all of which secrete normally 

 only a minute quantity of a serous fluid ; and 2. the synovial 

 membranes or capsules of the joints, the bursce mucosa? and sheaths 

 of tendons, which yield a viscid, yellowish material, the synovia, 

 which contains albumen and mucus. 



e. The corium. This consists of a dense, felt-like network of 

 bundles of connective tissue, which at the surface, and in the 

 papilla;, gives place to an indistinctly fibrillated, and partly, even, 

 more homogeneous tissue, and contains a great number of finer 

 and coarser elastic networks, also plasm-cells and numerous vessels 

 and nerves. The corium supports the cutaneous papillae on its ex- 

 ternal surface, and is here covered by the epidermis, with which it 

 forms the external integument ; and it is separated from the deeper 

 parts by a soft tissue generally rich in fat, the subcutaneous con- 

 nective tissue, or the adipose membrane (panniculus adiposus). 



f. The mucous membranes (tunica? mucosa?). These consist essen- 

 tially of a basis of connective tissue containing vessels and nerves — 

 the proper mucous membrane — of an epithelial layer covering it, 

 and of submucous connective tissue, which, in the intestine, is called 

 tunica nervea. The first is similar in structure to the corium, but 

 softer, and not unfrequently poor in elastic tissue and plasm-cells. 

 From the serous membranes the mucous membranes are, in general, 

 distinguished by their richness in vessels, their greater thickness, 

 their richness in glands, and their mucous secretion, which is chiefly 

 attributable to their soft epithelial covering ; yet there exist mucous 



