236 ELEMENTARY PHYSIOLOGY less. 



and so to form a bridge by which the bolus can travel 

 over the opening of the air-passage without any risk of 

 tumbling into it. While the epiglottis directs the course 

 of the mass of for>d below, and prevents it from pa.ssing 

 into the trachea, the soft palate guides it above, keeps it 

 out of the na.sal chamber, and directs it downwards and 

 backwards towards the lower part of the muscular pha- 

 ryngeal funnel. By this the bolus is immediately seized 

 and tightly held, and the muscular fibres contracting 

 above it, while they are comparatively lax below, it is 

 rapidly thrust into the oesophagus. 



The resophagus is lined with mucous membrane. This 

 rests on .some fibrous tissue, outside of which is a thick 

 coat of mu.scular tissue, striated in the upper third of the 

 tube, unstriated lower down next to the stomach. This 

 is arranged in two layers, an outer layer in which the 

 fibres run parallel to the long axis of the tube ; an inner 

 layer in which the fibres are wrapped round the tube. 



When food has been thrust into the ce.sophagus by the 

 action of the pharynx, the muscular wall of the oeso- 

 phagus just above the bolus contracts and pushes it 

 down into the next lower part. Then the wall of this 

 part contracts and pu.shes the mass a little further down 

 and so on. In this way the food is finally thrust into the 

 stomach by a .series of contractions of each part of the 

 oesophagus in succession : this is spoken of as peristaltic 

 action. 



Drink is taken in exactly the same way as food. It does 

 not fall down the pharynx and gullet, but each gulp is 

 grasped and passed down. Hence it is that jugglers are 

 able to drink standing upon their heads, and that a horse, 

 or ox. drinks with its throat lower than its stomach, feats 

 which would be impossiVjle if fluid simply fell down the 

 gullet into the gastric cavity. 



During these processes of mastication, insalivation, and 

 deglutition, what happens to the food is, first, that it is 

 reduced to a coarser or finer pulp : secondly, that any 



