GENERAL ANATOMY OF MUCOUS MEMBRANES. 65 



In some portions of the body, (as has already been observed, 

 vol. i. p. 438,) as in the nostrils, frontal and maxillary sinuses, 

 larynx, trachea, bronchia, vagina, uterus, fallopian tubes, &c. 

 the cylinders are surmounted with particular filiform organs, 

 called cilia, which are endowed with an undulating rotary action, 

 apparently independent of nervous influence, and which accord- 

 ing to Henle continue to act a short time after death. They 

 are supposed to carry onwards the fluids which cover them. 

 They constitute what is called the ciliary epithelium. 

 In some instances they have been seen attached to warty ex- 

 cresences belonging to the tesselated epithelium. 

 The mucous membranes vary in different parts in regard to 

 color from white to red, passing through all the intermediate 

 shades. They are red near their points of communication with 

 the skin, as in the pharynx and rectum ; of a pearl or pale 

 rose hue in the stomach ; and almost colorless in the centre 

 of the intestinal canal, except in cases where they have been 

 colored by disease or by the capillary injection which follows 

 asphyxia. 



The mucous membranes, are thrown in many places into a 

 number of loose folds, which amplify very considerably their 

 extent of surface. These folds may be seen in the nasal cavi- 

 ties, in the hollow organs in their undistended state as the sto- 

 mach and rectum where they are termed ruga, but particularly 

 in the small intestines, where they form an extensive series of 

 permanent doublings called the vahula cohniventes, or valves of 

 KerJcringius. 



The surface of the membrane presents in many places, a 

 superficial honey-comb-like appearance, which is discernable 

 only after close investigation in the stomach and gall-bladder in 

 man, but is strikingly developed in the alimentary canal of our 

 domestic animals, and in many fishes. 



All that is known in regard to the chemical analysis of mucous 

 membranes, is, that they are insoluble in water, even by boiling, 

 but are easy of solution in acids, with which they form a pulp. 

 These membranes, though possessed every where of many 

 characteristics common to the whole, vary somewhat in different 



