REFLEX OF SWALLOWING. 9 1 



The discharge of heat is, in man, chiefly dependent on the 

 circulation of the blood in the skin and subcutaneous 

 tissues, and on the secretion of sweat. Both of these pro- 

 cesses are presided over by nervous mechanisms of such a 

 nature that their activity varies with the surface tempera- 

 ture of the body. In animals (particularly in the dog) 

 the increased activity of the respiratory movements, which 

 is produced by increase of bodily temperature (see Influ- 

 ence of Nervous system on respiration), also serves as an 

 efficient means of regulation. 



The Reflex process of Swallowing. In the accomplish- 

 ment of the act by which food is conveyed from the fauces 

 into the stomach, the following changes take place : 



The larynx is drawn upwards under the tongue and 

 nearer to the hyoid bone, the epiglottis applying its upper 

 surface to the base of the tongue, and its under surface to 

 the larynx ; the glottis is closed ; the palato-pharyngeal 

 arches tighten and approach each other, without quite 

 meeting. The soft palate with the uvula is drawn back- 

 wards (by the combined action of the levatores and palato- 

 pharyngei), while the posterior wall of the pharynx 

 advances to meet it, and thus completely shuts off the 

 nares from the pharynx. The morsel as it glides down- 

 wards between the nearly even surfaces offered by the 

 tongue, epiglottis and cricoid cartilages in "front, and the 

 palato-pharyngeal arches behind, is at once seized by the 

 constrictors and carried onwards by their successive con- 

 tractions into the oesophagus. By a mode of action which 

 is called "peristaltic," and which resembles that of the 

 intestine and other muscular tubes, the food is conveyed 

 as far as the closed sphincter of the stomach. As soon as 

 this happens, the sphincter opens to allow of its entrance 

 into the stomach, closing again immediately. 



The centre which presides over this reflex process has its 

 seat in the medulla oblongata. It derives its most impor- 

 tant afferent influences from the mucous membrane of the 



