132 



SENSE OF TOUCH. 



on its parenchymal surface, and giving it shape and strength. This 

 serves as a foundation on which the epithelium rests. It may frequently 

 be demonstrated with very little trouble in the tubuli of the glands, 

 especially of the kidney, which are but very slightly adherent, by their 

 external surface, to the surrounding tissue. 



M. Flourens 1 considers that every mucous membrane is composed of 

 three laminae or layers, the derma, epidermis, and corpus mucosum 

 situate between the derma and epidermis. The corpus mucosum of 

 mucous membranes is continuous at all the outlets of the body, and is 

 identical with the second epidermis; differing, therefore, from the corpus 

 mucosum of the skin, a term which as elsewhere remarked he thinks 

 ought to be abolished. 



Histological examination exhibits the epithelium to consist of cells, 

 which are termed epithelial, and have various shapes. The two chief 

 are tesselated or pavement epithelium, and cylinder or conical epithe- 

 lium. Epithelium is not, however, confined to mucous membranes, 

 but, of late years, has been found to exist elsewhere; it is always 

 in contact with fluids, and of a soft, pliant cha- 

 racter. Tesselated epithelium covers the serous 

 and synovial membranes, the lining membrane of 

 the blood-vessels, and the mucous membranes, 

 except where cylinder epithelium exists. It is 

 spread over the mouth, pharynx and oesophagus, 

 conjunctiva, vagina, and entrance of the female 

 urethra. The cells composing it are usually po- 

 lygonal; and are well seen in the marginal figure. 

 Cylinder epithelium is found in the intestinal 

 canal, beyond the cardiac orifice, in the larger 

 ducts of the salivary glands, in the ductus com- 

 munis choledochus, prostate, Cowper's glands, 

 vesiculse seminales, vas deferens, tubuli uriniferi, 

 and urethra of the male ; and lines the urinary 

 passages of the female from the orifice of the 

 urethra to the beginning of the tubuli uriniferi 

 of the kidneys. In all these situations, it is continuous with tesselated 



Fig. 49. 



Fig. 48. 



Tesselated Epithelium. 



Extremity of one of the tu- 

 buli uriniferi, from the kidney 

 of an adult ; showing its tes- 

 selated epithelium. Magni- 

 fied 250 diameters. (Wagner.) 



Scales of Tesselated Epithelium. (After Henle.) 



A. Section of epithelium of conjunctiva with some scales loosened. B. Scales from surface of cheek, 

 c. The more deeply seated scales from the human conjunctiva. 



epithelium, which lines the more delicate ducts of the various glands. 

 The cells have the form of long cylinders or truncated cones, arranged 

 side by side, the apices attached to the mucous membrane or to flat 



Op. cit., p. 80. 



