48 



CILIATED EPITHELIUM. 



Fia 



Fy. 25. — Spheroidal 

 Ciliated Cells from 

 the biouth op the 

 Frog ; magnified 300 

 diameters. 



ejjitlielinm, which they resemble too in arrangement, but are 

 often of greater length and more slender and pointed at their lower 

 end, which is commonly branched. The cilia are attached to their 

 l.iroad 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 surftice of the 

 epithelial layer, as shown in fig, 25, whichre presents such cells from 

 the epithelium of the frog's mouth. In man 

 this form occurs in the ciliated epithelium of 

 the cerebral A-entricles and tympanum, where 

 the cells form but a single stratum. The co- 

 lumnar 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 divi- 

 sions — there is a layer of elongated cells beneath 

 the superficial ciliated range, filling up the 

 spaces between the pointed extremities of the 

 latter, and beneath this is an undermost layer, 

 formed of small rounded cells. Probably the 

 subjacent cells acquire cilia, and take the place of ciliated cells, which 

 are cast off; but the mode of renovation of ciliated epithelium is not 

 j'et fully understood. 



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

 tissue of the subjacent membrane, has much engaged attention since the 

 imi)ortance of the connective-tissue-corpuscles has come to be recognised ; and 

 a strong impression or belief prevails that such epithelium-cells are structurally 

 connected by prolongations from their lower ends with these corpuscles, and 

 genetically related to them. As a matter of observation, such anatomical con- 

 nection is affirmed in reference to the columnar ciliated epithelium of the central 

 canal of the spinal cord and the Sylvian aqueduct, (Lockliart Clarke, Gerlach). 



The cilia themselves differ widely in size in different animals, and 

 they are not equal in all parts of the same animal. In the human 

 windpipe they measure xiTW^h to -o Jooth of an inch in length ; but in 

 many invertebrate animals, es])ecially such as live in salt water, they 

 are _ a great deal larger. In figure they have the aspect of slender, 

 conical, or slightly flattened filaments ; broader at the base, and usually 

 pointed at their free extremity. Their substance is transparent, soft, 

 and flexible. It is to all appearance homogeneous, and no fibres, gran- 

 ules, or other indications of definite internal structure, have been satis- 

 factorily demonstrated in it. 



Motion of the cilia. — The manner in which the cilia move, is best 

 seen when they are not acting very briskly. Most generally they seem to 

 execute a sort of fanning or lashing movement ; and when a number of 

 them perform this motion in regular succession, as is generally the case, 

 they give rise to the appearance of a series of waves travelling along 

 the range of ciKa, like the waves caused by the wind in a field of corn. 

 When they are in very rapid action the undulation is less obvious, and, 

 as Henle remarks, their motion then conveys the idea of swiftly running 



