46 CILIATED EPITHELIUM. 



clear and colourless. It usually contains one or two nucleoli, distin- 

 guished by their stronjif dark outline ; and a variable number of more 

 faintly marked granules irregularly scattered. For the most part, the 

 nucleus is persistent, but in some cases it disappears from the cell. 



CILIATED EPITHELIUM. 



In this form of epithelium, the particles, which are generally co- 

 lumnar, bear at their free extremities little hau'-like processes, which 

 are agitated incessantly during life, and for some time after death, with 

 a lashing or vibrating motion. These minute and delicate moving 

 organs are named ciUa. They have now been discovered to exist very 

 extensively throughout the animal kingdom ; and the movements which 

 they produce are subservient to very varied purposes in the animal 

 economy. 



Distribution and use. — In the human 6ody ciliated epithelium 

 occurs in the following parts, viz. : — 1. On the mucous membrane of 

 the air passages and its prolongations. It commences at a little 

 distance within the nostrils, covers the membrane of the nose (except 

 the proper olfoctory part) and of the adjoining bony sinuses, and 

 extends up into the nasal duct and lachrymal sac. From the nose 

 it spreads backwards a certain way on the upper surface of the soft 

 palate, and over the upper or nasal region of the pharynx ; thence 

 along the Eustachian tube and lining membrane of the tympanum, of 

 which it covers the greater part. The lower part of the pharynx is 

 covered by scaly epithelium as already mentioned ; but the ciliated 

 epithelium begins again in the larynx a little above the glottis, and 

 continues throughout the trachea and the bronchial tubes in the lungs 

 to their smallest ramifications. 2. On the mucous lining and in the 

 glands of the uterus, commencing at the middle of the cervix and 

 extending along the Fallopian tubes, even to the peritoneal surface of 

 the latter at their fimbriated extremities. 3. Lining the vasa efferentia, 

 coni vascidosi, and first part of the excretory duct of the testicle. 4. 

 To some extent on the parietes of the ventricles of the brain, and 

 throughout the central canal of the spinal cord. 5. In the excretory 

 ducts of certain small racemose glands of various parts (tongue, 

 pharynx, &c.). 



In other mammiferous animals, as far as examined, cilia have been 

 found in nearly the same parts. To see them in motion, a portion of 

 ciliated mucous membrane may be taken from the body of a recently 

 killed quadruped. The piece of membrane is to be folded with its free 

 or ciliated surface outwards, placed on a slip of glass, with a little weak 

 salt water or serum of blood, and covered with thin glass. When it is 

 now viewed with a magnifying power of 200 diameters or upwards, a 

 very obvious agitation will be perceived on the edge of the fold ; this 

 appearance is caused by the moving cilia, with which the surface of the 

 membrane is covered. Being set close together, and moving simulta- 

 neously or in quick succession, the cilia, wlien in brisk action, give rise 

 to the appearance of a bright transparent fringe along the fold of the 

 membrane, agitated by such a rapid and incessant motion, that the 

 single threads which compose it cannot be perceived. The motion 

 here meant, is that of the cilia themselves ; but they also set in motion 

 the adjoining fluid, driving it along the cihated surface, as is indicated 

 by the agitation of any little particles that may accidentally float in it. 



