46 



DIGESTION. 



cation is pushed by the tongue against the palate, and so forced on 

 toward the fauces. 2d. As soon as the bolus enters the pharynx it 

 is pushed on by the tongue and by the contraction of the pillars 

 of the fauces and the constrictors of the pharynx toward the 

 oesophageal opening. The pharyngeal vault is guarded from in- 

 vasion by solid or liquid food by the valve-action of the soft palate, 

 while the opening of the glottis is protected by the simulta- 

 neous intrinsic muscular closure of the rima glottidis and by the 

 valve-like cover of the epiglottis. When the muscles of the fauces 

 and tongue push on the food-mass, they also draw up the larynx 

 and dilate the oesophageal opening. 3d. The oesophagus grasps the 

 food, and a peristaltic wave-series carries it rapidly on to the cardiac 

 opening of the stomach. The beginning (1st) of the act of swallow- 

 ing is voluntary, the remainder reflex, and is governed by centres in 

 the medulla oblongata acting through the cranial nerves which sup- 

 ply the parts. The trigeminus, glosso-pharyngeus, and vagus by 

 their sensory and motor functions act both in the capacity of affer- 

 ent and efferent communication with the medullary centre. 



Free Surface of the Gastric Mucous Membrane, viewed from above, from pig's stomach, 

 cardiac portion, moderately magnified. 



Describe the structure and function of the stomach. 



The stomach (Fig. 6) is an organ which resembles in structure 



