THE NERVOUS SYSTEM 519 



irritation caused by foreign bodies, of which the animal has no 

 knowledge, in consequence of sensation being lost. Division of 

 the superior maxillary branch in the horse — known as Bell's 

 experiment — prevents the animal from feeding, owing to in- 

 ability to grasp the food with its lips. Now, as this is a sensory 

 and not a motor nerve, the question arises, Why is the animal 

 prevented from grasping its food ? It is the duty of the sensory 

 branches of the fifth to keep the muscles informed of the position 

 of objects. When sensation is cut off, owing to the entire loss 

 of sensibility in the lips, the animal is unaware how to take hold 

 of the food. It can see the material in the manger, but, in conse- 

 quence of loss of sensation, does not know how to employ the 

 muscles of the lips to collect it. 



There are certain reflex acts in which the sensory branches 

 of the fifth are intimately concerned. When sensation is cut 

 off, the ' feelers ' growing from the orbit are unable to excite 

 the reflex act of closing the eye. Irritation of the Schneiderian 

 membrane produces no sneezing, and irritation of the conjunctiva 

 or cornea does not produce tears ; while the loss of sensation in 

 the tongue fails to stimulate the secretion of saliva. 



Ninth Pair, or Glosso -pharyngeal. —This nerve, consisting of 

 a motor and sensory portion, arises by several roots from the 

 anterior and lateral part of the bulb. As it leaves the 

 cranium, a ganglion is found on it — the ganglion petrosum. 

 This ganglion is connected with the superior cervical ganglion of 

 the sympathetic and the jugular ganglion of the vagus. There are 

 three branches of nerves distributed from the petrous ganglion : 

 one passes to the cavity of the tympanum, and supplies sensory 

 branches to the mucous membrane of the tympanum ; a second 

 is a motor nerve, and supplies the muscles of the pharynx ; while 

 the third branch is sensory, and supplies the posterior third of 

 the mucous membrane of the tongue, part of the pharynx, and 

 anterior face of the epiglottis. In this branch are taste fibres, 

 which end in the ' taste bulbs ' of the circumvallate papillae. 



Tenth Pair, or Pneumogastric— This is a mixed nerve, con- 

 taining motor, sensory, and secretory fibres. There is no nerve 

 possessing such a wide distribution, for its fibres extend from 

 the bulb to the anterior mesenteric ganglion in the abdominal 

 cavity. 



. The nerve arises from the floor of the fourth ventricle and the 

 nucleus of the solitary tract ; its motor fibres are derived from 

 the spinal accessory. Leaving the bulb, it passes through the 

 foramen lacerum, and here the sensory root has a ganglion on it, 

 the jugular ganglion. In conjunction with the spinal accessory, 

 the vagus courses its way on to the guttural pouch ; here the 

 two nerves separate. The vagus now joins with the cervical 



