CRANIAL NERVES. 443 



geal or recurrent nerve, which is given off by the pneumo- 

 gastric opposite the base of the heart, and ascends along 

 with the windpipe to the larynx, seems to have no function 

 connected with deglutition in the dog, but a very important 

 one in the case of the horse. In the latter animal, it con- 

 veys to the oblong medulla, the impressions made on the 

 mucous coat, and which lead, by a reflex action through the 

 pharyngeal and superior laryngeal nerves, to a vermicular 

 contraction of its muscular coat. Accordingly, it is found 

 that though no stimulation of this nerve can induce con- 

 tractions in the tracheal part of the gullet, its section on 

 both sides, or that of the pneumogastric nerves above their 

 origin, leads to a paralysed or ataxic condition of this part ; 

 so that when a pellet of food passes no contraction ensues. 

 Deglutition can still be effected through the power of the 

 pharyngeal muscles and those in front of the neck. In 

 the dog, section of the recurrent nerves does not in the 

 slightest interfere with the contractions of the oesophagus, 

 thus showing that the sensitive reflex filaments are in this 

 case contained in the pharyngeal and superior laryngeal 

 nerves. 



The thoracic portion of the gullet that between the 

 heart and stomach is supplied by twigs from the adjacent 

 trunks of the pneumogastric. If the latter, then, or the fila- 

 ments derived from it, are galvanised in the dead animal, a 

 vermicular contraction of the gullet takes place. Again, if 

 in the living animal the vagi be cut in the neck, and respi- 

 ration be meanwhile facilitated by performing tracheotomy, 

 the whole gullet is paralysed in the case of the horse ; and 

 though the animal may feed greedily, the aliments collect 

 along the whole length of the oesophagus, and can only be 

 passed on slightly when a new pellet is forced in by the 

 contractions of the pharnyx. In the dog, the thoracic por- 



