624 TEXT-BOOK OF PHYSIOLOGY 



2. The superior maxillary branch passes forward through the foramen 



rotundum, crosses the spheno-maxillary fossa, enters the infra-orbital 

 canal, and emerges at the infra-orbital foramen. In its course it 

 gives off a number of branches which are distributed as follows: viz., 

 to the integument and conjunctiva of the lower lid, the nose, cheek, 

 and upper lip, the palate, the teeth of the upper jaw, and the alveolar 

 processes. 



3. The inferior maxillary branch passes through the foramen ovale, after 



which it subdivides into three branches the auriculo- temporal, the 

 lingual, and the inferior dental. The ultimate branches are distributed 

 as follows: viz., the external auditory meatus, the side of the head, the 

 mucous membrane of the mouth, the anterior portion of the tongue, the 

 arches of the palate, the teeth and alveolar process of the lower jaw and 

 the integument of the lower part of the face. 



The afferent axons thus serve to bring into relation the skin, mucous 

 membranes of the head and face, and other sentient structures, with certain 

 sensor end-nuclei in the pons, medulla oblongata, and adjoining structures. 

 Cortical Connections. The afferent portion of the trigeminal nerve 

 is brought into physiologic relation with the sensor portion of the cerebral 

 cortex by means of nerve-fibers which have their origin in the cells around 

 which the terminal branches of the centrally coursing fibers arborize. The 

 cells situated in the substantia gelatinosa give off axons, which after a short 

 course cross the median line, enter the fillet and then ascend in the general 

 sensor tract to the cortex where they in turn arborize around sensor nerve- 

 cells. 



Properties. Irritative pathologic lesions, e.g., pressure by tumors, 

 aneurysms, neuritis, degenerative changes in the ganglion cells, or lesions 

 which in any way gradually impair the physical or chemic integrity of the 

 nerve-fibers, give rise to a variety of painful sensations referable to the seat 

 of the lesion or to one or more regions in the peripheral distribution of the 

 nerve. Many of the various forms of trigeminal neuralgia are caused by 

 lesions of this character. Exposure of the dental .nerves from caries of the 

 teeth, the presence of minute foreign bodies in the conjunctiva, operative 

 procedures in the nasal chambers, all testify to the extreme sensibility of the 

 nerve. Division of the large root within the cranium is followed at once by 

 complete abolition of all sensibility in the head and face to which its branches 

 are distributed. The skin and mucous membranes, the eye, nose, or teeth 

 may be experimentally injured without any evidences of pain on the part oi 

 the animal. Various reflexes, e.g., those of mastication, insalivation, degluti- 

 tion, the afferent paths of which are formed in part by the fifth nerve, are 

 often seriously impaired. At the same time the lachrymal secretion dimin- 

 ishes and the pupil contracts. The same results are observed in human 

 beings in whom the nerve has been divided for relief from severe neuralgia. 

 Anesthesia or a loss of sensibility may also be caused by pathologic lesions of 

 the nerve-trunks or of the sensor end-nuclei. 



Division of the large root at or near the ganglion of Gasser has not infre- 

 quently been followed by an alteration in the nutrition of the eye and nose. 

 In the course of twenty-four hours the eye becomes vascular and inflamed; 

 the cornea becomes opaque; and uteeration sets in, which may lead to com- 

 plete destruction of the eyeball. The mucous membrane of the nose be- 



