92 GENERAL ANATOMY OF THE TISSUES. 



tissue is transparent, contains fine elastic tissue in a more embryonic 

 state, and when boiled in water yields chondrin and not gelatine. 



d. The serous membranes consist of a connective tissue, rich in fine 

 elastic fibres, whose bundles anastomose, or are interwoven in different 

 modes ; and sometimes also, especially at the surface of these membranes, 

 appear more homogeneous. The serous membranes, which never possess 

 glands, and upon the whole but few vessels and nerves, line the cavities 

 which contain the viscera, and present an inner surface, which is smooth 

 and shining from the presence of an epithelial investment. They do not 

 necessarily form closed sacs, as was formerly believed, but may have 

 apertures in certain localities (abdominal apertures of the Fallopian 

 tubes), or may be wholly wanting, as upon the articular cartilages ; or 

 the areolar foundation may be absent, as in the so-called external lamina 

 of the arachnoidea cerebri. To these membranes belong I., the true 

 serous membranes, as the arachnoidea, the pleura, the pericardium, the 

 peritoneum, and the tunica vaginalis propria, which all, normally, 

 secrete only a minute quantity of serous fluid ; and 2, the synovial mem- 

 branes or capsules of the joints, bursce mucosce, and the tendinous 

 sheaths, which afford a viscid yellow secretion, the synovia contain- 

 ing albumen and mucus. 



e. The corium consists of a dense network of bundles of connective 

 tissue, which at the surface, and in the papillae, gives place to an indis- 

 tinctly fibrillated, in part even more homogeneous tissue, and contains a 

 great quantity of finer and coarser elastic networks, as well as very 

 numerous vessels and nerves. 



The corium supports the papillae upon its outer surface, and is here 

 covered by the epidermis, in connection with which it forms the external 

 skin ; from the deeper parts it is separated by a soft tissue, generally 

 very rich in fat, the subcutaneous connective tissue, adipose membrane, 

 or panniculus adiposus. 



f. The mucous membranes essentially consist of a very vascular basis 

 of connective tissue, well supplied with nerves, the proper mucous 

 membrane of an epithelial layer covering it, and of a submucous 

 areolar tissue, which in the intestine is also called the tunica nervea. 

 The former is of the same structure as the corium, only softer, and not 

 unfrequently ppor in elastic tissue. The mucous membranes are distin- 

 guished from the serous, in general by their greater vascularity, their 

 more considerable thickness, their numerous glands, and the mucous 

 secretion, which may be especially ascribed to their soft epithelium ; 

 though there are mucous membranes which are as delicate and glandless 

 as serous membranes ; and, on the other hand, the synovial capsules may 

 approximate the mucous membranes in their vascularity and the nature 

 of their secretion. The mucous membranes and the external skin are 

 analogous in all their principal components, whence the transitions 



