CHAP.XXITT.] DEGLUTITION. 189 



siderable muscular power, and a comparatively thick and insensible 

 lining membrane. 



On receiving the morsel forced into its upper orifice by the last 

 act of pharyngeal deglutition, the oesophagus is mechanically di- 

 lated, and its lining membrane stimulated by the contact. The re- 

 sult is a contraction of its muscular coat upon the pellet, which is 

 thereby carried forwards into the succeeding portions, in which the 

 like actions are induced, until it has traversed the entire canal. 

 This series of actions is rapid and quite involuntary ; but an obscure 

 sensation attends it, which is capable of being heightened to unea- 

 siness or pain if any obstruction be met with, or if the descending 

 morsel be too hot. It has been already stated that the contractions 

 are due to a central stimulus on the muscular nerves, derived from 

 the pressure of the food on those of the lining membrane (see p. 121). 

 It has been pointed out by Miiller that rapid and slight peristaltic 

 descending contractions occur in the oesophagus independent of the 

 passage of food. These are probably such as occur in the intestines 

 and uterus, without the accustomed stimulus and as a mere conse- 

 quence of their contractility. In vomiting, the oesophagus has an 

 inverted action, the muscular coat forcing up the food thrown into 

 it from below. In ruminating animals, this inverted peristaltic 

 motion is capable of being accomplished by the will, and a similar 

 power exists in some individuals among mankind, of which we have 

 witnessed more than one striking example. 



On passing a rapid series of electrical shocks down the oesophagus 

 of a dog just killed, the upper three-fourths of the tube are thrown 

 into continued or tetanic contraction, while the lower fourth takes 

 on a peristaltic or vermicular contraction ; thus demonstrating the 

 situation of the change from the striped to the unstriped fibres of 

 the muscular coat, according to the recent test of Weber. 



On the subject of the teeth, the student may conveniently refer to the 

 works of Leeuwenhoek, John Hunter, Thomas Bell ; Tomes, Med. Gaz. 1839 

 46 ; Owen, Odontography ; Nasmyth, on the Teeth ; Miiller's Physiology, by 

 Baly ; Goodsir, Ed. Med. and Surg. Journal, vol. 51. On insalivation, he may 

 consult Dr. Wright's works, which are of great interest and value. On deglu- 

 tition, Dzondi's observations, in Miiller, by Baly ; a paper by Mr. Ferguson, in 

 Med. Chir. Trans, vol. xxviii. p. 280 ; and the Cyclop. Anat., art. (Esophagus, 

 by Dr. Johnson. 



