CHAPTER VII.

TRIFACIAL, OR TRIGEMINAL NERVE.

Physiological anatomy of the trifacial-Properties and functions of the trifacial -Division of the trifacial within the cranial cavity-Immediate effects of division of the trifacial-Remote effects of division of the trifacial-Effects of division of the trifacial upon the organs of special sense-Division of the trifacial before and behind the ganglion of Gasser-Communication with the sympathetic at the ganglion of Gasser-Explanation of the phenomena of disordered nutrition after division of the trifacial-Cases of paralysis of the trifacial in the human subject.

A SINGLE nerve, the large root of the fifth pair, called the trifacial, or the trigeminal, gives general sensibility to the face and the head as far back as the vertex. This is one of the most interesting of the cranial nerves, and is one of the first that was experimented upon by physiologists. It is interesting, not only as the great sensitive nerve of the face, but from its connections with other nerves and its relations to the organs of special sense. In studying the physiology of this nerve, we must necessarily begin with its physiological anatomy.

Physiological Anatomy.-The apparent origin of the large root of the fifth is from the lateral portion of the pons Varolii, posterior and inferior to the origin of the small root, from which it is separated by a few transverse fibres of white substance. The deep origin is far removed from its point of emergence from the encephalon. The roots pass entirely through the substance of the pons, from without inward and from before backward, without any connection with the fibres of the pons itself. By this course it reaches the me

dulla oblongata, where the roots divide into three bundles. The anterior bundle passes from behind forward, between the anterior fibres of the pons and the cerebellar portion of the restiform bodies, to anastomose with the auditory nerve.' The other bundles, which are posterior, pass, the one in the anterior wall of the fourth ventricle to the lateral tract of the medulla oblongata, and the other, becoming grayish in color, to the restiform bodies, from which they may be followed as far as the point of the calamus scriptorius. According to Vulpian, a few fibres from the two sides decussate in the median line in the anterior wall of the fourth ventricle."

From this origin, the large root of the fifth passes obliquely upward and forward to the ganglion of Gasser, which is situated in a depression in the petrous portion of the temporal bone on the internal portion of its anterior face.

The Gasserian ganglion is semilunar in form (sometimes it is called the semilunar ganglion), with its concavity looking upward and inward. At the ganglion, the nerve receives filaments of communication from the carotid plexus of the sympathetic. This anatomical point is of importance in view of some of the remote effects which follow division of the fifth nerve through the ganglion in living animals.

It will be necessary only to describe in a general way

1 LUDOVIC HIRSCHFELD, Système nerveux, Paris, 1866, p. 166. The anastomosis of the auditory nerve has been denied (VULPIAN, Essai sur l'origine de plusieurs paires des nerfs craniens, Thèse, Paris, 1853, p. 27), but it is admitted by most anatomists.

2 Op. cit., p. 25.

3 The structure of this ganglion was first recognized by Gasser, Professor of Anatomy in Vienna. His observations, however, were published by Hirsch, a pupil of Gasser, in 1765 (HIRSCH, Paris quinti Nervorum encephali, Viennæ, 1765, in LUDWIG, Scriptores Nevrologici minores selecti, Lipsia, 1791, tomus i., p. 244, et seq.). Hirsch first gave it the name of Gasserian ganglion (p. 262). Some authors call it the Casserian ganglion, probably confounding Gasser with Casserius. Casserius, in his anatomical figures, describes many parts of the brain and nerves, but says nothing of the ganglion of the fifth (CASSERIUS, Anatomiche Tafeln, Franckfurt am Mayn, 1756).

the numerous branches of distribution of the fifth nerve, remembering that it is the great sensitive nerve of the face.

At the ganglion of Gasser, from its anterior and external portion, are given off a few small and unimportant branches to the dura mater and tentorium.

From the convex border of the ganglion, the three great branches arise that have given to the nerve the name of trifacial or trigeminal. These are: 1, the ophthalmic; 2, the superior maxillary; 3, the inferior maxillary. The ophthalmic and the superior maxillary branch are derived entirely from the sensory root. The inferior maxillary branch joins with the motor root and forms a mixed nerve.

The ophthalmic branch, the first division of the fifth, is the smallest of the three. Before it enters the orbit, it receives filaments of communication from the sympathetic, sends small branches to all of the motor nerves of the eyeball, and gives off a small recurrent branch which passes between the layers of the tentorium.

Just before the ophthalmic branch enters the orbit by the sphenoidal fissure, it divides into three branches; the lachrymal, frontal, and nasal.

The lachrymal, the smallest of the three, sends a branch to the orbital branch of the superior maxillary nerve, passes through the lachrymal gland, to which certain of its filaments are distributed, and its terminal filaments go to the conjunctiva and the integument of the upper eyelid.

The frontal branch, the largest of the three, divides into the supra-trochlear and supra-orbital nerves. The supratrochlear passes out of the orbit between the supra-orbital foramen and the pulley of the superior oblique muscle. It sends in its course a long, delicate filament to the nasal branch, and is finally lost in the integument of the forehead. The supra-orbital passes through the supra-orbital foramen, sends a few filaments to the upper eyelid, and supplies the forehead, the anterior and median portions of the scalp, the

mucous membrane of the frontal sinus, and the pericranium covering the frontal and parietal bones.

The nasal branch, before it penetrates the orbit, gives off a long, delicate filament to the ophthalmic ganglion, constituting its sensory root. It then gives off the long ciliary nerves, which pass to the ciliary muscle and iris. Its trunk then divides into the external nasal, or infra-trochlearis, and the internal nasal, or ethmoidal. The infra-trochlearis is distributed to the integument of the forehead and nose, to the internal surface of the lower eyelid, the lachrymal sac, and the caruncula. The internal nasal is distributed to the mucous membrane, and also in part to the integument of the nose.

The superior maxillary branch of the fifth passes out of the cranial cavity by the foramen rotundum, traverses the infra-orbital canal, and emerges upon the face by the infraorbital foramen. Branches from this nerve are given off in the spheno-maxillary fossa and the infra-orbital canal, before it emerges upon the face. In the spheno-maxillary fossa, the first branch is the orbital, which passes into the orbit, giving off one branch, the temporal, which passes through the temporal fossa by a foramen in the malar bone, and is distributed to the integument on the temple and the side of the forehead; another branch, the malar, which likewise emerges by a foramen in the malar bone, is distributed to the integument over this bone. In the spheno-maxillary fossa, are also given off two branches, which pass to the sphenopalatine, or Meckel's ganglion. From this portion of the nerve, branches are given off, the two posterior dental nerves, which are distributed to the molar and bicuspid teeth, the mucous membrane of the corresponding alveolar processes, and to the antrum.

In the infra-orbital canal, a large branch, the anterior dental, is given off to the teeth and mucous membrane of the alveolar processes not supplied by the posterior dental nerves. This nerve anastomoses with the posterior dental.

The terminal branches upon the face are distributed to

the lower eyelid (the palpebral branches); to the side of the nose (the nasal branches), anastomosing with the nasal branch of the ophthalmic; and to the integument and mucous membrane of the upper lip (the labial branches).

The inferior maxillary is a mixed nerve, composed of the inferior division of the large root and the small root. The distribution of the motor filaments has already been described under the head of the nerve of mastication.' This nerve passes out of the cranial cavity by the foramen ovale, and then separates into the anterior division, containing nearly all of the motor filaments, and the posterior division, which is chiefly sensory. The sensory portion breaks up into numerous branches:

1. The auriculo-temporal nerve supplies the integument in the temporal region, the auditory meatus and the integument of the ear, the temporo-maxillary articulation, and the parotid gland. It also sends important branches of communication to the facial.

2. The lingual branch is distributed to the mucous membrane of the tongue as far as the point, the mucous membrane of the mouth, the gums, and to the sublingual gland. This nerve receives an important branch from the facial, the chorda tympani, which has already been described. From this nerve, also, are given off two or three branches which pass to the submaxillary ganglion, constituting its sensory roots.

3. The inferior dental nerve, the largest of the three, passes in the substance of the inferior maxillary bone, beneath the teeth, to the mental foramen, where it emerges upon the face. The most important sensory branches are those which supply the pulps of the teeth, and the branches upon the face. The nerve, emerging upon the face by the mental foramen, called the mental nerve, supplies the integument of the chin and the lower part of the face, the lower lip, and sends certain filaments to the mucous membrane of the mouth.