and only rarely vertical. When the eye vibrates in one plane, it ordinarily moves outward quickly and more slowly returns. The oscillations vary in number from fifty to two hundred or more a minute, and in extent from one to ten millimeters. In uremic coma the eyes will sometimes be noticed in a rhythmical movement which carries them through their widest lateral range about ten times a minute. Nystagmus may be constant or only provoked by calling forth a particular movement of the eyes, as by directing them upward or outward. This latter must not be confused with the jerky, unrhythmical, and momentary movements of weakened muscles. It may

The causes and significance of nystagmus are often obscure. be acquired as the sequel of any condition which greatly impairs vision, Corneal and lenticular opacities, choroiditis, and retinitis may precede it, especially if occurring in childhood. Albinos frequently present nystagmus. Miners who work in cramped positions with poor illumination acquire it, probably as a fatigue neurosis through the overstrain of certain eye-muscles in attempting to keep the work in view. In them it is often only present when the particular attitude which their work requires is assumed.

Nystagmus is present incidentally or regularly in a long list of nervous diseases which have neither location nor pathological anatomy in common. It is almost a cardinal symptom in insular sclerosis and in hereditary ataxia of the Friedreich type. It is common in cerebellar tumor and tumors involving the corpora quadrigemina and optic thalami. Occasionally it attends sinus thrombosis, meningitis, meningeal hemorrhage, and variously seated cerebral hemorrhages, softenings, and tumors. Hysteria has also furnished rare cases of persistent nystagmic ocular

spasm.

The treatment of ocular palsies depends upon the causal condition and is often most unsatisfactory. New growths and traumata are surgical conditions for the most part. Syphilitic palsies may readily vield to treatment, whether due to basilar or central involvement, but only too often recur, yield again, and finally become permanent. The neuritic form is treated as a part of the general intoxication usually at the bottom of the disease. A persisting ocular deviation is often benefited by a tenotomy. Muscle cutting should always be preceded by exercise of the muscles with prisms, which sometimes is helpful, and by general treatment. Nystagmus, excepting in the unusual cases where it is due to meningeal and sinous diseases, or other curable lesion, is practically unyielding to all measures. Miners' nystagmus usually ceases when the occupation is changed.

CHAPTER VI.

DISEASES OF THE TRIFACIAL NERVE.

Anatomical Considerations.-The fifth nerves represent the sensory portions of all the motor cranial nerves. Their sensory distribution embraces most of the skin of the head and face, all their mucous membranelined cavities, and the cerebral meninges in part. In addition, through at least the chorda tympani, the fifth subserves the special sense of taste. Its small motor root innervates the mandibular muscles of mastication. The nuclear origin of the fifth nerve in the medulla is correspondingly extensive. The smaller motor nucleus is situated under the floor of the fourth ventricle near its lateral angle, with an upward extension as high as the corpora quadrigemina. Outside of this is the larger sensory nucleus, which is connected continuously with nuclear gray matter as low as the fourth cervical spinal segment. These centra are brought into relation with the cerebellum and with the cerebral cortex by upward radiations. For the motor portion the cortical centers are at the foot of the anterior central convolution. The sensory cortical representation is not clearly known. The sensory and motor trunks leave the surface of the pons separately, though side by side, and only after the sensory portion has passed through the Gasserian ganglion does the motor trunk join the third trigeminal division.

The strictly gustatory portion follows a most extraordinary course before, as the chorda tympani, it reaches the lingual nerve and is distributed to the anterior portion of the tongue. At first contained in the sensory trunk, it apparently passes from the Gasserian enlargement with the middle or superior maxillary branch. Thence it drops into the sphenopalatine or Meckel's ganglion, and turns backward in the form of the Vidian nerve, to penetrate the petrous portion of the temporal bone and join the facial nerve in the Fallopian aqueduct. It follows the facial nearly to its exit at the stylomastoid foramen, where it turns sharply upward, reaching the tympanic cavity, which it leaves by the Gasserian fissure. It then descends between the pterygoid muscles and joins the lingual branch of the inferior maxillary or third trifacial division, to be distributed to the anterior portion of the tongue. The base of the tongue and faucial pillars also recognize taste impressions. It is supposed that these sensations reach the trunk of the fifth by way of the glossopharyngeal nerve through connections with Meckel's ganglion. We know certainly that division of the sensory trunk of the fifth abolishes all taste sensation on the corresponding side of the oral and pharyngeal cavities.

Cortical Diseases of the Fifth Nerve.-Lesions of the portion of the motor cortex associated with the fifth nerve produce spasm or paralysis according as the lesion is irritative or destructive. The involved muscles are the pterygoids, the temporal, and the masseter.

In generalized convulsions they are ordinarily involved. Very rarely they are the sole seat of motor disturbance presenting a masticatory spasm or paralysis. The spasm may be tonic, as in trismus, or repeated at varying intervals. The teeth are tightly clenched, and the masseters and temporals stand out firm and hard. In the clonic variety, as in the chattering of a chill, the lower jaw is sharply moved laterally or vertically. Vigorous grinding of the teeth may be present. This is sometimes seen in the late stages of paretic dementia and in other wide-spread organic brain disease. Single or repeated spasms may have their origin in local disease of the jaws, such as periosteitis or toothache, and are then reflexly produced.

Masticatory paralysis of cortical origin is extremely rare. The cortical lesions have almost invariably been found to be bilateral, but

Fig. 38.-Distribution of the sensory cutaneous nerves on the head: V1, V2, V3, The three branches of the trigeminus; at, auriculotemporal; so, supraorbital; st, supratrochlear; it, infratrochlear; 1, lacrymal; m, mental; b, buccinator; am, auricularis magnus; sm, subcutaneous male; oma, occipitalis major; omi, occipitalis minor; cs, superficial cervical (after Hirt).

Hirt1 has reported a case of complete mandibular palsy due to a leftsided lesion at the foot of the ascending frontal convolution.

Nuclear disease of the fifth nerve is usually a part of a group of bulbar symptoms. Masticatory paralysis arising from this source is extremely rare. Progressive bulbar palsy and pontine tumors may cause it, but other cranial nerves are almost invariably affected at the same time. Multiple sclerosis and tabes may and often do affect the fifth nucleus, causing bilateral sensory and motor symptoms in the area of its distribution.

Peripheral intracranial affections of the trigeminus may involve the stem, the Gasserian ganglion, or the three branches of the nerve at their exits from the skull. The differential diagnosis as to location may

1 "Berlin. klin. Wochens.," 1887.

be impossible if adjoining nerves or structures are uninjured or present no indications. A description of the symptoms arising from injury to the trunk will therefore apply to disease of the Gasserian ganglion or of the three branches at their cranial exits. Growths and imflammatory processes are the usual causes of this form of trifacial disease.

The motor symptoms are those of paresis or paralysis of the mandibular muscles. The jaws can not be closed or can not be firmly held together when closed. The combined strength of the jaw-muscles is immense, and considerable impairment may go unnoticed. In complete bilateral paralysis the jaw droops, but can at first be raised by the action of the facial muscles, especially the buccinators and orbicularis oris. If the palsy is one-sided, the jaw may still be raised by the unilateral action of the uninjured side, but the bite is feeble. Attempts to bring the paralyzed pterygoids into play fail to produce grinding movements, so that the jaw can not be forcibly advanced from the impaired side or thrust in the opposite direction. In long-standing cases contracture in the muscles which depress the jaw may permanently hold the mouth open.

Fig. 39.-Case of nuclear disease of the fifth cranial nerve in a case of tabes, showing area of cutaneous anesthesia; some facial atrophy is also present.

Interference with sensation may be partial or complete. In the latter case all parts of the face, head, nasal fossæ, conjunctivæ, mouth, and tongue supplied by the fifth nerve are insensitive, and taste is abolished on that side of the tongue and oral cavity. Prodromal pricking, tingling, and burning usually precede the anesthesia. Frequently, when the loss of sensation is pronounced, so that the patient no longer feels a pinprick, complaints are made of pain and burning in the anesthetic area,anæsthesia dolorosa. In one case observed by the writer, while general sensation was abolished in all its modes and tenses, muscular sense remained. A touch or prick was not perceived, but the slightest motion communicated to any facial muscle was instantly recognized, apparently through the uninjured seventh nerve. Trophic disturbances are the rule, but, ordinarily, they are slight in degree. The insensitive conjunctiva and cornea are easily irritated and prone to ulceration that may reach a destructive grade. The nasal and lacrimal secretions are defective and the mucous membrane dry. In the nose this dryness impairs the sense of smell. The paralyzed side of the tongue is thickly furred, due partly, but not wholly, to the fact that food is only chewed on the sound side. The salivary secretion may be greatly diminished. Herpetic eruptions in the cutaneous distribution are frequent, and when the ganglion or branches are diseased and the conjunctiva is involved, con

stitute a serious feature, as ophthalmia and complete loss of the eye may

ensue.

Facial hemiatrophy may follow injury and disease of the fifth nerve. In this rare deformity the wasting is always limited to the distribution of the trifacial, and is usually

most intense in the field of the middle and inferior divisions. The alleged causes in numerous instances, such as blows on the head and face, infectious fevers, exposure to cold, facial erysipelas, osteitis of the jaws, etc., are capable of seriously influencing the nerve. In two cases histological changes in the trunk, ganglion, or branches have been demonstrated, and it has followed division of the root of the trigeminus in man and animals. It may begin in a widening sclerodermic patch on the side of the face, but more commonly the entire half of the face gradually diminishes. The loss affects both dermal and osseous structures and less markedly the muscles, which may escape entirely. Sensory disturbances are common, and in certain instances severe pain is felt. The opposite side of the face may finally become involved, though this is rare. The disease develops usually before adult life, but may appear at any age. It produces a most notable difference of appearance on the two sides. The atrophic half lacks the proportions of the sound side in every particular. The condition is usually most marked in the lower portion of the face, gradually lessening upward so that the brow may show almost no discrepancy on the two sides. The skin is thinned notably, sometimes to a half or quarter of its proper thickness; the muscles are sometimes reduced in size and strength; the lower jaw may be a third smaller on the affected side. The teeth are often lost. As the skin is closely applied to the muscles and the bony conformation, a cadaverous appearance is presented that may be strikingly at variance with the plump, healthy side, and is sometimes sharply marked by a furrow at the middle line of the brow and chin. The nose, chin, and mouth deviate to the affected side. While the orbital and palpebral structures are frequently wasted, the eyeball is affected only in rare cases, but has been observed wasted and even destroyed. The disease is progressive for years, but may come to a standstill at any time, and again advance. It seems to be unmodified by treatment.

Their

Disease of the trifacial branches is extremely common. course through bony channels, serving to protect them admirably under ordinary conditions, exposes them to pressure from inflammatory states, to injury by concussing blows, and to laceration from fractures involving the cranial and facial bones. Their proximity to the nasal,