CILIATED EPITHELIUM. 



But the extent and limits of the ciliated epithelium of the human body have 

 been determined chiefly from its anatomical characters. 



Cilia have now been shown to exist in almost every class of animals, 

 from the highest to the lowest. The immediate purpose which they serve 

 is, to impel matter, generally more or less fluid, along the surfaces on which 

 they are attached ; or, to propel through a liquid medium the ciliated 

 bodies of minute animals, or other small objects on the surface of which 

 cilia are present ; as is the case with many infusorial animalcules, in which 

 the cilia serve as organs of locomotion like the fins of larger aquatic animals, 

 and as happens, too, in the ova of many vertebrate as well as invertebrate 

 animals, where the yelk revolves in its surrounding fluid by the aid of cilia 

 on its surface. In many of the lower tribes of aquatic animals, the cilia 

 acquire a high degree of importance : producing the flow of water over the 

 surface of their organs of respiration, indispensable to the exercise of that 

 function ; enabling the animals to seize their prey, or swallow their food, 

 and performing various other offices of greater or less importance in their 

 economy. In man, and the warm-blooded animals, their use is apparently to 

 impel secreted fluids or other matters along the 

 ciliated surface, as, for example, the mucus of 



Fig. XXIX. 



the windpipe and nasal sinuses, which they 



carry towards the outlet of these cavities. 



The cells of the ciliated epithelium contain 

 nuclei, as usual ; they have most generally an 

 elongated or prismatic form (fig. xxix.), like 

 the particles of the columnar epithelium, which 

 they resemble too in arrangement, but are 

 often of greater length and more slender and 

 pointed at their lower end. The cilia are 

 attached to their broad or superficial end, 

 each columnar particle bearing a tuft of these 

 minute hair-like processes. In some cases, the 

 cells are spheroidal in figure, the cilia being 

 still, of course, confined to that portion of the 

 cell which forms part of the general surface of 



the epithelial layer, as shown in fig. xxx., which represents such cells from 

 the epithelium of the frog's mouth. In man this form occurs in the ciliated 

 epithelium of the cerebral ventricles and tympa- 

 num, where the cells form but a single stratum. 

 The columnar ciliated epithelium also may exist as 

 a simple layer, as in the uterus and Fallopian tubes, 

 the finest ramifications of the bronchia, and the 

 central canal of the spinal cord ; but in various 

 other parts as the nose, pharynx, Eustachian 

 tube, the trachea and its larger divisions there 

 is a layer of elongated cells beneath the superficial 

 ciliated range, filling np the spaces between the 

 pointed extremities of the latter, and beneath 

 this is an undermost layer, formed of small 

 rounded cells (fig. xxxi.). Probably the sub- 

 jacent cells acquire cilia, and take the place of 

 ciliated cells which are cast off ; but the mode of 

 renovation of ciliated epithelium is not yet fully understood. 

 The relation of the ciliated, as well as other epithelium-cells, to the connective tissue 



Fig. XXIX. COLUMNAR 

 CILIATED EPITHELIUM-CELLS 

 FROM THE HUMAN NASAL 

 MEMBRANE; MAGNIFIED 300 

 DIAMETERS. 



Fig. XXX. 



Fig. XXX. SPHEROIDAL 

 CILIATED CELLS FROM 

 THE MOUTH OP THE 

 FROG ; MAGNIFIED 300 



DIAMETERS. 



