EPITHELIUM. 213 



the subjacent membrane, are treated with water, they seem to be 

 surmounted by a delicate membrane. This is, however, merely a 

 continuous sheet formed by the ends of the cells ; they having been 

 separated by the endosmosis of the water. (Fig. 150.) 



B. Compound Conoidal Epithelium. 



This variety consists of two or more layers of cells, the outer- 

 most being conoidal. It is shown by Figs. 151 and 152. Where- 

 ever found it is always ciliated. 



Fig. 152. 



Fig. 151. Simple conoidal ciliated epithelium, a. Nucleated cells. &. Cilia and their free extre- 

 mities. 



Fig. 152. Compound conoidal ciliated epithelium of nasal passages, a. Superficial series of ciliated' 

 cells. 6. Deeper series becoming elongated vertically, c. Various shapes of deepest ciliated cells. 

 (180 diameters). 



Distribution. Commencing about three-quarters of an inch within 

 the nostrils, it extends through the nasal passages, covers the upper 

 part of the pharynx and posterior surface of the soft palate; then 

 enters the larynx to line that, the trachea, and the bronchial tubes 

 to their finer subdivisions. It also lines the Eustachian tube, and; 

 the lachrymal duct and sac. 



Ciliated Epithelium. 



Epithelium is so called when the outer layer of cells are sur- 

 mounted by cilia. These, seen under the microscope, resemble 

 very fine hairs, and the average number attached to each cell is 10 

 to 22. ( Valentin?) They grow from the free (or outer) extremity of 

 the cells, and are generally so arranged as nearly to cover it, though 

 sometimes but a single one is found. They are fine, soft processes 

 of the cell membrane, broader at their base and terminating in a 

 point. They are in incessant motion; constantly striking forward 

 from a vertical position to very nearly a horizontal one, and in- 

 stantly returning again. The author counted one hundred and 

 forty such strokes in a minute, in case of cells from the pharynx of 



