The distribution and peripheral connections of this nerve are somewhat complicated, and should be carefully studied when the manifold functions of its branches are being considered. The various impulses conveyed by the trifacial nerves may be thus enumerated:

(1) EFFERENT FIBRES.

1. Motor. To the muscles of (1) mastication, viz., temporal masseters, both pterygoids, mylohyoid, and the anterior part of the digastrics; (2) to the tensor muscle of the soft palate; and (3) to the tensor tympani. (4) In some animals (rabbit) nerve filaments are said to pass to the iris, reaching the eyeball by the ciliary ganglion.

2. Secretory. The efferent impulses which stimulate the cells of the lachrymal gland to increased action pass along the branches of the ophthalmic division of this nerve.

3. Vasomotor. The nerves governing the muscles of the blood vessels of the eye, of the lower jaw, and of the mucous membrane of the cheeks and gums.

4. Trophic. On account of the impairment of nutrition of the eye and mucous membrane of the mouth, which occurs after injury of fifth nerve, it is said to carry fibres which preside over the trophic arrangements of these parts.

(2) AFFERENT FIBRES.

1. Sensory. All the divisions of the trifacial nerve may be said to be connected with cutaneous nerves, by which the ordinary sensory impulses are carried from-(1) the entire skin of the face, and the anterior surface of the external ear; (2) from the external auditory meatus; (3) from the teeth and periosteum of the jaws, etc.; (4) from the mucous membrane lining the cheeks, floor of the mouth, and anterior part of the tongue; (5) from the lining membrane of the nasal cavity; (6) from the conjunctiva, ball of the eye, and orbit generally; (7) and from the dura mater including the tentorium.

2. Excito-motor.-Some of the fibres which have just been enumerated as carrying ordinary sensory impressions have special powers of exciting coördinated reflex motions. Thus the sensory

fibres from the conjunctiva and its neighborhood are the afferent channels in the common reflex acts of winking and closing the eyelids; and the fibres from the nasal mucous membrane excite the involuntary act of sneezing.

3. Excito-secretory.—As in the case of reflex movements, secretion may be excited reflexly. Fibres carry afferent impulses to the medulla from the anterior part of the tongue, and excite activity of the salivary glands. Stimulation of the mucous membrane of the nose or eye causes impulses to pass to the secretory centre of the lachrymal glands, which are frequently thus reflexly excited.

Intense stimulation of almost any of the afferent nerves may excite these reflex phenomena. Thus the most stoic person will experience active secretions of saliva and lachrymal fluid, as well as spasmodic closure of the lids during the extraction of a tooth. Even the bold use of a blunt razor will cause tears to flow down the cheeks, by sending excito-secretory impulses along the branches of the inferior and superior maxillary division of this

nerve.

4. Tactile impulses are appreciated by the anterior part of the tongue with remarkable delicacy, and are conveyed by the lingual branch of the fifth nerve; most of the cutaneous fibres are also capable of receiving tactile stimulation.

5. Taste. The tastes appreciated by the anterior part and the edges of the tongue are carried by fibres which lie in the peripheral branches of this nerve. These belong chiefly, if not altogether, to the chorda tympani, and leave this lingual branch of the fifth to join the seventh nerve on their way to the trunk of the glosso-pharyngeal.

There are four ganglia in close relation to the branches of the fifth nerve which have certain points of similarity, and may, therefore, be considered together, although their positions show that they are engaged in the performance of very different functions.

We have not yet been able to ascertain the value of these little points of junction of motor, sensory, vasomotor, and secretory fibres, because, so far, we are unable to attribute to the cells of

the ganglia either reflecting or controlling action, or any automatic power.

They all have efferent (motor and secretory) and afferent (sensory) connections with the nervous centres, and also connections with the main channels of the sympathetic nerves. These are spoken of as the roots of the ganglia. Their little branches are generally mixed nerves.

THE CILIARY OR OPHTHALMIC GANGLION.

This ganglion lies in the orbit. It has three roots, which come from-(1) the inferior oblique branch of the third nerve, by a short slip, which forms the motor root; (2) from the nasal branch of the ophthalmic division of the fifth, and (3) from the carotid plexus of the sympathetic. The branches go mostly to the ball of the eye, and may be divided into afferent and efferent. The afferent are sensory branches, connecting the cornea and its neighboring conjunctiva with the centres. The efferent fibres go to the iris and cause dilatation of the pupil (coming mostly from the sympathetic), and the vasomotor fibres going to the choroid coat, iris, and retina.

THE SPHENO-PALATINE OR NASAL GANGLION.

This lies on the second division of the fifth nerve, from which it gets its sensory root. Its motor root comes from the seventh by the great superficial petrosal nerve, and its sympathetic root from the carotid plexus by the branch joining this nerve. These enter the ganglion together, and are spoken of as the vidian nerve. Afferent (sensory) impulses, from the greater part of the nasal cavity, pass through this ganglion. Its efferent branches are-(1) motor to the elevator of the soft palate and azygos uvulæ; (2) vasomotor, which comes from the sympathetic; and (3) secretory, which supply the glands of the cheek, etc.

OTIC OR EAR GANGLION.

The otic ganglion lies under the foramen ovale, where the interior division of the fifth comes from the cranium. Its roots are (1) motor; (2) sensory, from the inferior division of the fifth;

and (3) sympathetic, made up of a couple of fine filaments from the plexus, around the meningeal artery. By its branches it communicates with the seventh, chorda tympani, and sends filaments to the parotid gland.

THE SUBMAXILLARY GANGLION.

This is on the hyoglossus muscle in close relation to the lingual branch of the fifth, from which it gets a sensory root. The chorda tympani passes to the ganglion, carrying efferent impulses through it to the gland. Its sympathetic branches come from the plexus around the facial artery.

VIII THE GLOSSO-PHARYNGEAL NERVE.

This nerve forms part of the eighth pair, and springs from the floor of the fourth ventricle above the nucleus of the vagus. It is a mixed nerve, the functions of which may be thus classified:— Afferent fibres, which are of various kinds, viz.:

(1) Sensory fibres, carrying impulses from the anterior surface of the epiglottis, the base of the tongue, the soft palate, the tonsils, the Eustachian tube and tympanum.

(2) Excito-motor. This nerve excites important reflex movements in swallowing and vomiting, when a stimulus is applied to the glosso-palatine arch.

(3) Excito-secretory, the stimulation of the back of the tongue gives rise to a copious flow of saliva by means of reflex action.

(4) Taste sensations are, for the most part, carried by this nerve; they are conveyed from special nerve endings in the back of the tongue (see Taste).

The efferent fibres are not so varied, being simply motor to the middle constrictor of the pharynx, stylo-pharyngeus, elevator of the soft palate, and the azygos uvulæ.

THE SPINAL ACCESSORY NERVES.

These also form part of the eighth pair of nerves, and arise from the medulla oblongata and spinal cord, as low down as the seventh cervical vertebra. The lower fibres leave the lateral columns at their posterior aspect, and then run up between the

denticulate ligament and the posterior roots of the spinal nerves to enter the cranial cavity. On their way out of the cranium they divide into two parts, one of which becomes amalgamated with the vagus, and the other passes down the side of the neck as the motor nerve of the sterno-mastoid and trapezius muscles. Physiologically, it may be compared with the anterior root of a spinal nerve, and the part accessory to the vagus probably supplies that nerve with most of its motor branches.

THE VAGUS NERVE.

The vagus arises from the lower part of the floor of the fourth ventricle, and is connected with many of the important groups of nerve cells in this neighborhood.

The functions of its widely-distributed fibres may be thus briefly stated:

(A) The EFFERENT FIBRES may be divided into

1. Motor-nerve channels, going to a great portion of the alimentary tract and air passage; the following muscles getting their motor supply from the branches of the vagus-the pharyngeal constrictors, some muscles of the palate, œsophagus, stomach and greater part of the small intestine. Motor impulses also pass along the trunk of the vagus-though leaving the cord by the roots of the accessory nerve--to the intrinsic muscles of the larynx; these fibres lie in the inferior or recurrent laryngeal nerve, except that to the crico-thyroid, which lies in the superior laryngeal branch. The tracheal muscle and the smooth muscle of the bronchial walls are also under the control of the pulmonary branches of the vagus.

2. Vasomotor fibres are said to be supplied to the stomach and small intestine. These fibres are probably derived from some of the numerous connections with the sympathetic.

3. Inhibitory impulses of great importance for the regulation of the forces of the circulation pass along the vagus to the ganglia of the heart. As already explained in detail (see page 280), these fibres are always acting, as shown by the fact that section of the vagi causes a considerable quickening of the heart beat. On the other hand, if the distal end of the cut vagus be stimu