24:4: HANDBOOK OF PHYOLOGY. 



the oesophagus. Between the outer and inner layers of the muscular coat, 

 nerve-ganglia of Auerbach are also found. 



DEGLUTITION" OR SWALLOWING. 



When properly masticated, the food is transmitted in successive por- 

 tions to the stomach by the act of deglutition or swallowing". This, 

 for the purpose of description, may be divided into three acts. In the 

 first, particles of food collected to a morsel are made to glide between 

 the surface of the tongue and the palatine arch, till they have passed the 

 anterior arch of the fauces; in the second, the morsel is carried through 

 the pharynx; and in the third, it reaches the stomach through the oesoph- 

 agus. These three acts follow each other rapidly. (1.) The first act 

 may be voluntary, although it is usually performed unconsciously; the 

 morsel of food, when sufficiently masticated, being pressed between the 

 tongue and palate, by the agency of the muscles of the former, in such a 

 manner as to force it back to the entrance of the pharynx. (2.) The 

 second act is the most complicated, because the food must pass by the 

 posterior orifice of the nose and the upper opening of the larynx without 

 touching them. When it has been brought, by the first act, between the 

 anterior arches of the palate, it is moved onwards by the movement of 

 the tongue backwards, and by the muscles of the anterior arches contract- 

 ing on it and then behind it. The root of the tongue being retracted, 

 and the larynx being raised with the pharynx and carried forwards under 

 the base of the tongue, the epiglottis is pressed over the upper opening" 

 of the larynx, and the morsel glides past it; the closure of the glottis 

 being additionally secured by the simultaneous contraction of its own 

 muscles, so that, even when the epiglottis is destroyed, there is little 

 danger of food or drink passing into the larynx so long as its muscles 

 can act freely. At the same time, the raising of the soft palate, so that 

 its posterior edge touches the back part of the pharynx, and the approx- 

 imation of the sides of the posterior palatine arch, which move quickly 

 inwards like side curtains, close the passage into the upper part of the 

 pharynx and the posterior nares, and form an inclined plane, along the 

 under surface of which the morsel descends; then the pharynx, raised up 

 to receive it, in its turn contracts, and forces it onwards into the oesoph- 

 agus. (3.) In the third act, in which the food passes through the 

 oesophagus, every part of that tube, as it receives the morsel, and is di- 

 lated by it, is stimulated to contract; hence an undulatory contraction 

 of the oesophagus, which is easily observable in horses while drinking, 

 proceeds rapidly along the tube. It is only when the morsels swallowed 

 are large, or taken too quickly in succession, that the progressive con- 

 traction of the oesophagus is slow, and attended with pain. Division of 

 both pneumogastric nerves paralyzes the contractile power of the cesoph- 



