DIGESTION 159 



soit palate, and in the most favourable position to be applied 

 over the glottis ; it has also been shown that when the head is 

 extended the epiglottis is in the mouth — viz., anterior to the soft 

 palate. We have found it in this position in the horse, and 

 judging from the fact that in a state of nature the horse and ox 

 swallow with an extended and not with a flexed neck, it is 

 probable that in feeding off the ground the epiglottis is anterior 

 to the soft palate. During the third stage of deglutition the 

 bolus can be seen slowly travelling down the channel of the neck ; 

 if liquid, however, be passing, the movement is very rapid, for 

 as many as sixty swallows may be made in a minute. Both 

 in eating and drinking the third act of deglutition can occur 

 against gravity ; this is because it is a muscular act. The whole 

 process of deglutition is considerably assisted by the salivary 

 secretion. When this has been experimentally diverted, swallow- 

 ing only occurs with difficulty and very slowly. 



It is now generally recognised by physiologists that the passage 

 of material along the oesophagus depends upon its consistency : 

 if fluid, it is shot along from end to end by the one act of swallow- 

 ing, whereas, if it is solid material, it passes along by the process 

 of peristalsis. The wave begins behind the pharynx, the cir- 

 cular muscle contracts, and its action is helped by the immedi- 

 ately preceding contraction of the longitudinal muscle, which 

 thereby shortens, and so tends to dilate the tube for the recep- 

 tion of the bolus. In man liquids may be shot into the stomach 

 in 01 second, but solid material is believed to occupy 6 seconds 

 for the peristaltic wave to reach the stomach. Judging from 

 the rate of progress of a bolus along the cervical portion of 

 the oesophagus of the horse, 3 or 4 seconds might be occupied 

 from pharynx to stomach ; and taking into consideration the 

 far greater length of the oesophagus as compared in man, it 

 would appear that the rate of peristalsis is quicker in man. In 

 rumination, as we shall see, the rate is very quick, ij seconds 

 from pharynx to stomach. 



The oesophagus of the horse is found to differ considerably 

 from that of most other animals. It is composed for the greater 

 part of its length of red striated muscle, while at and near its 

 termination the previously thin muscular coat becomes very 

 thick and rigid, and the red gives way to pale, non-striped 

 muscle ; further, the lumen of the tube becomes very narrow. 

 The thick terminal end of the oesophagus of the horse is always 

 closely contracted, so that if cut through close to the stomach 

 no material can escape ; this is one explanation why horses vomit 

 with such difficulty. In the ox, sheep, and dog, the tube is 

 composed of red muscle throughout ; it terminates in a dilated 

 end at the stomach, and, owing to its thin, distensible walls, 



