THE ENCEPHALIC OR CRANIAL NERVES 637 



some of which terminate in fine end-tufts around nerve-cells in the sub- 



stantia gelatinosa. 



2. ^ The Peripheral Branches. The peripheral axons emerge from the 

 peripheral end of the ganglion of Gasser in three distinct and separate 

 branches, each of which is distributed to a different region of the face 

 and head. 



1. The ophthalmic branch passes forward and subdivides into three large 



branches, the frontal, the lachrymal, and the nasal. The ultimate 

 termination of the branches of these nerves is as follows: viz., the 

 conjunctiva and skin of the upper eyeb'd, the cornea, the skin of the 

 forehead and the nose, the lachrymal gland and caruncle, and the 

 mucous membrane of the nose. 



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 of 



