CHAP, vi.] THE CAPS ALIMENTARY SYSTEM. 175 



Its epithelium is squamous, except on the hinder surface of the 

 velum palati, and in the upper (or nasal) region of the pharynx, where 

 we meet with CILIATED EPITHELIUM. This very remarkable tissue 

 consists of epithelial particles nucleated cells generally columnar 

 in form, each having, freely projecting from its surface, from six to 

 thirty thread-like processes, each from TT ,'- - If to ^V<r of an inch 

 in length (Fig. 11), like miniature human eye -lashes whence 

 their name. 



These minute processes have the wonderful property of performing 

 constantly during life, and (in a warm atmosphere) for as much as 

 forty-eight hours after death, repeated lashing movements ; each 

 cilium Lending itself with great rapidity, and then becoming more 

 slowly straightened. ^ All the adjacent cilia move in the same 

 direction, thus producing a wave-like motion similar to that of a 

 field of corn under a strong wind. 



The result of these multitudinous and constantly-repeated minute 

 motions each repeated about ten times in a second is to propel 

 small particles along the ciliated surface of the body. 



If a ciliated cell be detached, so as to float freely in some suitable 

 fluid, then the effect of this action of its cilia is to move about the 

 cell itself as by a sort of locomotion. Water checks the action of 

 cilia, but blood will preserve it even for two or three days ; such 

 action still continuing on slips of membrane detached from the 

 body. No muscular tissue and no nerve has been detected in the 

 ciliated cells, nor are the actions of the cilia amenable to nervous or 

 moderate electrical influence. They persist in the membrane which 

 bears them when this is detached. The cause of their motion is 

 as yet utterly inexplicable, an ultimate mystery like that of the 

 contractile power of muscular tissue. 



The FUNCTION OF THE PHARYNX is to direct the food which has 

 just been pushed, through the isthmus faucium, downwards towards 

 tbe stomach by means of successive contractions of its fibres from 

 above downwards. It becomes more powerfully grasped as it 

 approaches the oesophagus. This active prehension of aliment 

 equally takes place when that aliment is fluid, none being allowed 

 simply to fall down towards the stomach while the walls of the 

 alimentary tract remain passive. 



12. The gullet, or (ESOPHAGUS, is a narrow, cylindrical tube, 

 beginning at the bottom of the pharynx and extending downwards 

 through the diaphragm, to terminate (immediately it has passed 

 through that partition) in the stomach. It extends along above the 

 trachea and heart, and beneath the vertebral column and longus colli 

 muscle, being connected with those parts by lax areolar tissues. 



It is, of course, lined with mucous membrane, the surface of 

 which is covered with squamous epithelium. 



The mucous membrane of the upper part of the oesophagus is 

 folded (when the passage is not distended) in a number of vertical 

 folds. 



The lower end of the oesophagus, for a short distance before 



