Chap. 1 1 i.i EPITHELIUM 21 



mis. The cell protoplasm is more transparent in the 

 former, and the granular cells of the stratum granu- 

 losum are not always present, but they generally are 

 in the epithelium of the tongue and of the rest of the 

 oral cavity. The most superficial scales show more or 

 less horny transformation. 



23. Stratified columnar epithelium is met 

 with on the lining membrane of the respiratory 

 organs, as larynx, trachea, and large bronchi. It 

 consists of several layers of columnar cells : a super- 

 ficial layer of conical or prismatic cells, with a more 

 or less pointed extremity directed towards the depth , 

 between these are inserted spindle-shaped cells, and 

 finally inverted conical cells. 



The epithelium of the ureter and bladder is called 

 transitional epithelium. It is stratified, and the most 

 superficial layer consists of squamous cells. Under- 

 neath this is a layer of club-shaped cells, between 

 which extend one or more layers of small spindle- 

 shaped cells. 



Amongst the columnar epithelial cells occurring 

 in man and mammals the ciliated cells and the goblet 

 cells, and amongst the squamous cells the prickle cells, 

 deserve special attention. 



24. Ciliated cells are characterised by possess- 

 ing a bundle of very fine longer or shorter hairs or 

 cilia on their free surface. These cilia are direct pro- 

 longations of the cell protoplasm. More correctly 

 speaking, the cilia are continuous with the filaments 

 or strise of the cell protoplasm. The superficial layer 

 of conical cells of the epithelium in the respiratory 

 organs, the columnar cells lining the uterus and ovi- 

 duct, and the columnar cells lining the tubes of the 

 epididymis possess such cilia. In lower vertebrates 

 the ciliated cells are much more frequently observed ; 

 in Batrachia the epithelial cells lining the mouth, 

 pharynx, and oesophagus are ciliated. 



