10 



PHYSIOLOGY OF MUSCLES A^'D ^'ERYES. 



7. If a light powder — such, for instance, as finely 

 powdered charcoal — is spread over the skin of the 

 palate of a living or a recently killed frog, the powder 

 is seen to advance with some speed towards the gullet. 

 Microscopic examination shows that this skin is studded 

 with a dense layer of cylindrical cells standing, palisade- 

 like, side by side. The free surface of each of these 

 cells is studded with a large number of delicate hairs 



Fig. 3. 

 a. Ciliated cells, pointed be- 

 low, and, with other cells, 

 attaclied to the mem- 

 brane. 



b. A single ciliated cell, more 

 enlarged ajid of some- 

 what more modified form. 



or cilige, which are in continual motion in a definite 

 direction in such a way that they propel all such liquid, 

 together with the particles contained in this, as adheres 

 to their upper surface in that direction. This is calle(f 

 ciliary motion. It occurs very frequently in the animal 

 body, e.g. in the windpipe and its branches, where the 

 motion is upward, serving to propel the phlegm to the 

 larynx, from which it can be thrown out by coughing. 



