fectly recognized; but in the higher degrees of anesthesia all colors merge into a uniform sepia tint. Another important fact has been pointed out by Landolt, viz., that the eye on the same side as the lesion participates, though to a less extent, in the loss of color-perception.

Clinical Deductions drawn from Preceding Pages. Amblyopia of one eye can result from lesions involving the optic nerve in front of the chiasm, or possibly (?) from lesions of the internal capsule. If from the latter, the field for colorperceptions will be found to be markedly contracted or colorvision will be wanting; both eyes may be affected, the most marked changes being found, however, in the eye opposite to the seat of the lesion.

Hemianopsia may occur when the occipital lobes (chiefly the cortex of the cuneus), Wernicke's tract, the pulvinar of the thalamus, the optic tracts, or the optic chiasm are pressed upon or destroyed by lesions of, or in the region of, the cerebrum. It is evident, therefore, that the trephine cannot always afford relief of this symptom. When syphilitic gummata may be suspected, the prognosis is extremely favorable if active treatment be employed. The variety of hemianopsia often indicates the seat of the lesion with great exactness.

If paralysis (in any of its forms) coexist with hemianopsia, a valuable guide will often be afforded in determining the extent of the lesion.

Crossed paralysis of the "olfactory nerve and body type" indicates a localized pressure which is chiefly exerted upon parts within the anterior fossa of the skull. The motor tract is probably involved by upward pressure upon the caudate or lenticular nucleus, or the fibers of the internal capsule, thus accounting for the hemiplegia of the opposite half of the body. The olfactory nerve, which lies near to the optic chiasm, is affected by pressure in the downward direction, and the optic chiasm or tract may be simultaneously involved; hence a loss of smell in the nostril on the same side as the lesion may coexist with some form of hemianopsia, as well as with a crossed hemiplegia.

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Crossed paralysis of the "motor-oculi nerve and body" type indicates a lesion situated within the crus cerebri. If hemianopsia be present in connection with this condition, it proves conclusively that the optic tract, which lies in close relation with the crus, is simultaneously affected by the lesion. We find, therefore, that the eye on the same side as the lesion is blind in its temporal half if the optic tract be involved; that it can no longer be turned toward the nose or made to act in parallelism with the opposite eye; that the pupil is dilated; and that the upper eyelid droops over the eyeball, giving it a sleepy appearance. On the side opposite to the lesion the eye is blind in its nasal half, and the body is hemiplegic. There are few conditions which are of greater clinical importance than this type of crossed paralysis, because the seat of the lesion is positively indicated.

Choked disk is a common symptom of lesions of the base of the cerebrum, and of any intra-cranial disease which produces a gradually increasing pressure. It is specially diagnostic of tumors. It is not associated with impairment of vision until late, so that it is often unsuspected when present. The ophthalmoscope is necessary for its detection. It may coexist with hemianopsia, and is always bilateral. It is a positive contra-indication to trephining.

Lesions at the base of the skull may cross the mesial line, and still involve only one optic tract. If this occurs, the hemianopsia will be accompanied by other symptoms of diagnostic importance, no longer confined to one side. Double anosmia, general paresis or complete paralysis, general anæsthesia, and paralytic symptoms referable to both eyeballs, might be thus produced. Lesions of this character are more liable to affect the chiasm of the optic nerves than the optic tracts; in either case, however, hemianopsia would result, and its type would be a reliable guide to the seat of pressure (see Fig. 43).

Crossed paralysis of the "facial nerve and body type" is not as liable to coexist with hemianopsia as the two forms previously mentioned. The reason for this is a purely ana

tomical one. The symptoms of facial paralysis are too involved to be given here in detail.

Uncomplicated hemianopsia indicates that no pressureeffects are exerted upon the motor or sensory projection tracts, or adjacent nerves.

Aphasia sometimes coexists with hemianopsia. I have met with two instances of this kind. In one there was slight paresis of the left side, tending to prove that aphasia can occur with lesions involving the right hemisphere. Both were cured with specific treatment. We must attribute the development of this complication to pressure upon parts in the neighborhood of Broca's center, or to lesions of the internal capsule, where the speech tract comes in close relation to the optic fibers (Fig. 39).

Lesions confined to the crus cerebri seldom create impairment of any of the special senses excepting that of the sight. These cases are not associated with impairment of intellect or usually of speech. It has been claimed that severe lesions cause paralysis of the bladder, but I have never encountered it. Many points of interest pertaining to lesions of the crura will be considered later.

THE CRURA CEREBRI.

If, after the removal of the brain from the skull, the base of the cerebrum be examined, the adjacent parts being left intact (Fig. 28), it will be perceived that the crura cerebri emerge from the upper border of the pons Varolii, diverge from one another, and then disappear in the cerebral hemispheres, passing beneath the optic tracts. A space is thus left between the crura, in which may be seen the so-called "posterior perforated space" (where the vessels enter the brain to supply the optic thalamus), and the "corpora mamillaria” (Fig. 37), which are formed by the anterior pillars of the fornix.

On the inner aspect of each crus, near to the angle of divergence from its fellow, may be noticed several bundles of

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fibers which issue from its substance to form the third cranial or "motor-oculi" nerve of the corresponding side. The groove, from which these bundles escape, may be considered as an external indication of the separation of the fibers contained within the crus into two bundles (the "basis cruris," or "crusta," and the "tegmentum cruris"), which we have already discussed (Fig. 45). The larger portion of the crus, which lies anterior to this groove, is the "crusta"; while the "tegmentum" is the smaller or posterior portion.

If a cross-section of the crus be now made, it will be perceived (Fig. 45) that the crusta and tegmentum are separated by a tract of dark-colored gray substance, the "substantia

FIG. 45.-A diagrammatic representation by the author of the parts seen in a horizontal cross-section on a level with the superior quadrigeminal body.

c. q., corpora quadrigemina; S. N., substantia nigra; R. N., red nucleus; S., aqueduct of Sylvius, surrounded by its gray matter; q. t., tract of trigeminus nerve root (quintus tract); p. l. f., posterior longitudinal fasciculus.

nigra" of Soemmering. This collection of nerve cells comes to the surface, on the inner aspect of the crus, at a point which corresponds to the escape of the fasciculi of the third cranial nerve (the sulcus oculo-motori), and, on the outer

aspect of the crus, along a grooved line (the lateral sulcus). The construction of the two main subdivisions of the crus and its collections of gray matter must be considered separately.

THE CRUSTA OR BASIS CRURIS (proper cerebral peduncle). This portion of the cerebral peduncle lies ventrad of the substantia nigra, and is formed almost entirely of bundles of fibers running longitudinally, and continuous below with those of the pons Varolii and medulla oblongata (Fig. 8). It is semilunar in section-the concave surface of the substantia nigra projecting into it (Fig. 45).

Those bundles which lie adjacent to the substantia nigra are smaller than the rest and are partially separated by processes of this gray mass (left half of Fig. 45). They have been named by Meynert the "stratum intermedium." Their origin and termination differ from those of the bundles which lie more anteriorly. They serve to connect chiefly the cells of the substantia nigra with the reticular formation of the pons and medulla, although a few pass upward to join the lenticular nucleus (Meynert).

The main tracts of the crusta are a direct prolongation downward of fibers of the internal capsule of the cerebrum (Fig. 8) and corona radiata. These fibers are continuous below with those of the anterior pyramids of the medulla oblongata, at the lower part of which ganglion the majority of the bundles decussate and pass down the lateral columns of the opposite side of the spinal cord as the "crossed pyramidal tracts" (Fig. 46). The ganglia of origin are possibly the nucleus caudatus and the nucleus lenticularis, but more probably the cells of the motor cerebral gyri.

The bundles which are situated in the lateral or outer part of the crusta are stated by Meynert to present peculiarities of origin and distribution. He believes that the fibers which compose these bundles arise from the occipital, parietal, and temporo-sphenoidal lobes of the cerebrum (the sensory area), and enter the crus without any apparent connection with the cells of the basal ganglia; that they decussate in the