DIGESTION. 51) 



along the oesophagus to enter the stomach. This stage is performed 

 by the intrinsic contractions of the muscular fibers of the oesophagus- 

 walls. As is known, its muscular fibers are arranged in two layers: 

 one circular, the other longitudinal. The upper third is composed of 

 striated muscle-fibers, the lower two-thirds of plain, or unstriped, 

 variety. Accordingly in the upper third the movement of the bolus 

 is more rapid than in the lower two-thirds. The movement through 

 the oesophagus is that known as peristaltic,, or vermicular. The sec- 

 ond and third stages of deglutition are involuntary. When the death- 

 rattle occurs it is caused by the pharynx not contracting around the 

 bolus. 



Swallowing of Fluids. 



From what has been said previously it will be readily perceived 

 that the act of deglutition of both liquids and solids is a muscular 

 act, and not, therefore, dependent upon gravity. Thus, horses and 

 many other animals drink with their heads low, so that the fluid must 

 needs be forced up an inclined plane to reach their stomachs. Some- 

 times jugglers, while standing upon their heads, perform the feat of 

 drinking. 



The deglutition of boli or food was, for convenience, divided 

 into three stages, but so quickly is the passage of liquids accomplished 

 that physiologists are able to recognize but one movement. We are 

 indebted to the experiments and observations of Kronecker and 

 Meltzer for an explanation of this process; according to them, there 

 is an action resembling, in the main, that of a force-pump, whereby 

 the mass of liquid is propelled with extreme rapidity through the 

 pharynx and oesophagus. 



It is by the contraction of the two myloliyoids that the liquid 

 is put under high pressure and shot along in the direction of least 

 resistance : through the pharynx and oesophagus. This pair of mus- 

 cles is greatly aided by the simultaneous action of the two hyoglossi 

 muscles. These two pairs of muscles, by acting in unison, form a 

 sort of diaphragm to push the root of the tongue backward and down- 

 ward, at the same time performing a force-pump action upon the 

 liquid to be swallowed. So quickly is the passage of the liquid accom- 

 plished that the pharyngeal and cesophageal muscles have not time to 

 contract about the mass of liquid; in fact, they are inhibited during 

 the passage of liquids through their respective channels. After the 

 liquids arrive in the stomach the act of deglutition ensues for the pur- 

 pose of removing the liquids adhering to the walls of oesophagus. 



