40 
ANIMAL PATHOLOGY. 
tongue, and is finally lost among the follicles and the substance 
of the dorsum of the tongue. 
The Function of the ninth pair of Nerves . — This nerve is evi- 
dently connected with or presides over the deglutition of the food 
— the first act of it at least, its conveyance to the commencement 
of the oesophagus. The food having been sufficiently triturated, 
or needing no trituration, is conveyed to the posterior part of the 
mouth, in order to be swallowed ; for this purpose the mouth is 
closed by the action of the muscles of the jaws, the anterior 
part of the tongue is elevated, and the posterior depressed ; and 
the pharynx is expanded, and the epiglottis is laid down, and the 
food sliding over the dorsum of the tongue enters the pharynx ; 
the isthmus of the fauces is closed against its return, and the 
constrictor muscles of the pharynx seize upon it and urge it on- 
ward until it enters the commencement of the oesophagean tube. 
This process is performed as readily and as accurately by the 
foal and the calf as by the full-grown animal, and is performed 
on fluid substances, far more difficult to be swallowed than those 
that are solid. And how is all this accomplished ? By the in- 
fluence of the glosso-pharyngeal nerve ; by pure organic influence. 
But are there not many voluntary musles concerned in the 
action ? there are : their assistance was obtained before the will 
began to exert its power: these voluntary muscles then obeyed 
another influence ; they were the servants of the principle of 
organic life. An association was formed which the will could 
afterwards assist or suspend, but not always break, except at the 
hazard or destruction of life. 
The excito-motory System . — This has been satisfactorily ex- 
plained by Dr. Marshall Hall. The voluntary muscles can and 
do act independently of the will in the performance of certain 
offices essential to life. There are certain sets of nerves, organic 
nerves, which are not only acted upon by certain stimuli in the 
discharge of the functions of life, but which have the power of 
calling upon other nerves, more or less under the influence of the 
will, to assist them in the full or more perfect discharge of their 
duty. The glosso-pharyngeal is one of these excitor nerves, and 
the act of deglutition is performed more by the influence of those 
motor nerves which it can call to its aid than by its own inherent 
power. The nerve is excited by the pressure of the food on its 
superficial filaments. It responds to the stimulus and acts, but 
the effect of that stimulus is conveyed to the medulla oblongata; 
it is reflected thence to the source of other nerves, and all the ap- 
propriate muscles of deglutition are excited to action. It is thus 
alone that we can account for the action of many a voluntary 
