THE CRANIAL NERVES. 223 



nerve, viz. : the ophthalmic, the superior maxillary and the inferior 

 maxillary. 



Distribution. The centrally directed branches enter the pons 

 Varolii on its lateral aspect. After pursuing a short distance, these 

 fibers arborize around nerve-cells in the gray matter of the pons 

 and medulla. 



The peripherally directed branches are distributed as follows : 



1. The ophthalmic branches to the conjunctiva and skin of the upper 

 eyelid, the cornea, the skin of the forehead and the nose, the 

 lachrymal gland and the mucous membrane of the nose. 



2. The Superior maxillary branches to the skin and conjunctiva 

 of the lower lid, the nose, the cheek and upper lip, the palate 

 teeth of the upper jaw and the alveolar processes. 



3. The inferior maxillary branches to the external auditory meatus, 

 the side of the head, the mouth, the tongue, the teeth of the lower 

 jaw, the alveolar processes and the skin of the lower part of the 

 face. 



Properties. The trigeminal nerve, composed mainly of afferent 

 fibers, is the most acutely sensitive nerve in the body, and endows all 

 the parts to which it is distributed with general sensibility. 



Irritation of the large root, or of any of its branches, will give rise 

 to marked evidence of pain ; the various forms of neuralgia of the 

 head and face being occasioned by compression, disease, or exposure 

 of some of its terminal branches. 



Division of the large root within the cranium is followed at once 

 by a complete abolition of all sensibility in the head and face, but is 

 not attended by any loss of motion. The integument, the mucous 

 membranes, and the eye may be lacerated, cut, or bruised, without 

 the animal exhibiting any evidence of pain. At the same time the 

 lachrymal secretion is diminished, the pupil becomes contracted, the 

 eyeball is protruded, and the sensibility of the tongue is abolished. 



The reflex movements of deglutition are also somewhat impaired, 

 the impression of the food being unable to reach and excite the nerve 

 center in the medulla oblongata. 



Origin of the Efferent Fibers. The efferent fibers have their 

 origin in nerve-cells in the gray matter of the pons Varolii beneath 

 the floor of the fourth ventricle. 



Distribution. The efferent fibers, known collectively as the small 

 root, emerge from the side of the pons Varolii, pass forward beneath 



