£58 A MANUAL OF VETERINARY PHYSIOLOGY 



the second stage the act is complex, for the bolus or fluid has to 

 cross the air passage, and must be prevented from falling into 

 the nasal chambers, or finding its way down the trachea. To 

 accomplish this the soft palate is raised and so closes the nasal 

 chambers, the tongue at the same time being carried backwards, 

 while the larynx and pharynx are advanced. This movement 

 causes the base of the tongue to press on the epiglottis and close 

 the larynx, which is further secured by the arytenoid cartilages 

 and vocal cords coming close together. The bolus, liberally 

 coated with mucus from the large mucous crypts in this locality, 

 or fluid, can now safely pass towards the pharynx, being grasped 

 by the pharyngeal muscles and pressed into the oesophagus. 

 In the third act of swallowing the food is carried down the oeso- 

 phagus by a continuous wave of contraction, which starts at 

 the pharynx and ends at the stomach. Chauveau points out 

 that, owing to its extreme length, the soft palate of the horse 

 passes completely into the pharynx during the second act of 

 deglutition. The length of the soft palate in this animal prevents 

 food or water being returned by the mouth when once they have 

 entered the pharynx, so that in vomiting, or in cases of sore 

 throat, the food, water, or other material is returned by the 

 nostrils. 



It is now considered that in some animals the constrictor 

 muscles of the pharynx take less share in the process of swallowing 

 than was at one time supposed, and that the sharp contraction 

 of the mylo-hyoid muscles of the tongue, together with a back- 

 ward movement of the organ, exerts pressure on the bolus, and 

 shoots the latter through the pharynx into the oesophagus. From 

 the time the mylo-hyoids act until the entrance of the food 

 into the oesophagus, only a second elapses. We are not inclined 

 to think these observations can at present be applied to swallow- 

 ing in the horse. If the hand is placed in the pharynx there is 

 no suggestion of any such shooting movement, and material, 

 such as a bolus, placed far back on the tongue, is frequently 

 very deliberate in entering the oesophagus. 



The action of the epiglottis in the closure of the glottis has been 

 much discussed. In the horse it is forced over the opening 

 by the base of the tongue and the advancing larynx ; but the 

 epiglottis is not essential to swallowing, for an animal can swallow 

 when it has been removed, and even when one of the arytenoid 

 cartilages has been excised. With a finger in the larynx it can 

 easily be demonstrated that the part closes tightly and forcibly 

 during the second stage of swallowing, the vocal cords and ary- 

 tenoids being brought so close together that the glottis is perfectly 

 air-tight. It has been pointed out that animals usually swallow 

 with a flexed neck, as in this position the epiglottis is behind the 



