mo A Mciwdl of Veterinary Physiology. 



paratively a slow process, the passage of liquid, on the 

 other hand, is very rapid. As many as sixty movements 

 may be made in a minute, the motion being capable of 

 occurring against gravity — for example, when an animal 

 drinks from the ground. 



The process of swallowing solids is facilitated by the saliva. 

 Thus, when the salivary secretion lias been experiment- 

 ally diverted, swallowing only occurs with difficulty and 

 very slowly. 



The upper portion of the oesophagus for two-thirds of its 

 length is composed of striped muscular fibre, though not 

 under the control of the will ; the lower or posterior third 

 consists of unstriped muscle and is exceedingly thick. 



The nervous mechanism employed in swallowing is very 

 complicated. The swallowing centre, which is situated in 

 the medulla and pons Varolii, has to be stimulated, and the 

 muscles employed have to act regularly and in their proper 

 order. 



The reflex act of swallowing is as follows : By means of 

 the sensory glossopharyngeal and superior laryngeal nerves 

 an impression is conveyed to the brain of the presence of 

 material in the pharynx : a motor impression is then sent 

 out, putting in action the motor fibres of the glosso- 

 pharyngeal supplying the muscles of the pharynx, and 

 causing them to contract. 



The tongue is supplied with sensation by the glosso- 

 pharyngeal, and portions of the fifth pair ; the pharynx 

 by the glossopharyngeal, and the opening into the larynx 

 by the superior laryngeal. The motor nerves of the tongue 

 are the hypo-glossal, inferior maxillary division of the fifth 

 and branches of the facial. The palate is supplied by the 

 pharyngeal plexus formed by the vagus, glosso-pharyngeal, 

 andsympathetic ; the glosso-pharyngeal supplies the muscles 

 of the pharynx with motor powers, and the branches of the 

 fifth supply the muscles of mastication. 



In ruminants swallowing is carried on by the same 

 physiological process. Both the mouth and pharynx are 

 very large and wide, and the oesophagus of considerable 



