by a broad dorsal commissure, above which is a commissure of the acustico-lateralis centers lying under the lateral extensions of the cerebellum. They are enveloped on all sides by tracts of fibers running vertically between the cerebellum and the regions in the brain stem below and cephalad of the nuclei, the cerebellar tracts forming a sort of capsule around the grey nuclei, these relations being the same as already described for cyprinoids. The relations of this nucleus and its tracts are shown in Fig. 37.

The intrinsic neurones of these nuclei are rarely well impregnated in my GOLGI preparations. The fibers of the central gustatory path end for the most part in free arborizations among these cells without crossing. But some of the tract fibers are clearly seen to cross to the opposite nucleus through the commissure of the secondary gustatory nuclei, as MAYSER has stated.

The tertiary tract arises from the chief cells in the cortical portions of the nucleus. These are frequently impregnated Fig. 37. A parasagittal section taken through the brain of Ameiurus nebulosus so cut as to pass through about the middle of one vagal and one facial lobe and the lateral part of the cerebellum (cf. Figs. 5 and 20). Drawn from a single

GOLGI preparation. X 45.

The section shows nearly the whole course of the central gustatory path (sec.gust.t.), composed of neurites of the chief secondary gustatory neurones of the vagal and facial lobes which terminate in the secondary gustatory nucleus (s.g.n.) under the cerebellum. The origin of the facial portion of the descending secondary gustatory tract (desc.sec. VII.) is seen in the facial lobe. In the facial lobe there is also seen a portion of the lateral part of the communis root of the facial nerve (com.VII) passing up to arborize within the lobe. The neurones of the vagal and facial lobes, which were richly impregnated in the preparation, are omitted from the drawing for the sake of simplicity. Along the cephalic border of the secondary gustatory nucleus is the beginning of the secondary gustatory commissure (s.g..). The origin of the tertiary gustatory tract from the secondary nucleus is not shown, but the terminations of these fibers (gust.3) are illustrated in the inferior lobe.

Bundles of fibers from the tuberculum acusticum are seen under the facial lobe, where they decussate, and their termini in the nucleus lateralis mesencephali (torus semicircularis or colliculus) are also shown (sec. VIII). Under the cerebellum are the cerebellar tracts which envelop the secondary gustatory nucleus (c). Granules of the cerebellum are marked gr.; those of the valvula, g. The bodies of the Purkinje cells of the cerebellum are indicated by dotted outlines. nuc.com., is the commissural nucleus of CAJAL.

and are of the same type as in cyprinoids. Their neurites, mingling with the tractus lobo-cerebellaris, pass down to end in the inferior lobe of the same side, essentially as already described for the carp. The ventral portion of this tract and its terminal arborizations are seen in Fig. 37.

The return path in the oblongata by way of the tractus lobo-bulbaris is also essentially as described for the carp.

SECTION V. SUMMARY AND GENERAL CONCLUSIONS.

In this section a brief summary of the facts as described in the preceding pages is followed by a discussion of some of the morphological considerations growing out of them.

The teleostean fishes generally possess taste buds freely scattered over the mucous surfaces of the mouth, gills and lips. The group of Ostariophysi is characterized by a very great development of this system of sense organs-in the siluroids in the outer skin and barblets and in the cyprinoids both in the outer skin and in still greater degree in the palatal organ within the mouth.

It has previously been shown experimentally that these fishes do in reality taste with their cutaneous taste buds, which are often called terminal buds and which have no relationship whatever with any variety of lateral line organs. Furthermore, while pure cutaneous gustatory stimuli can be localized by the fish, ordinarily both gustatory and tactile stimuli cooperate in the discrimination and localization of food objects.

The distribution and innervation of the organs of taste have been accurately determined for the siluroid fish, Ameiurus, all of them being innervated by the communis system of peripheral nerves. The nerves from the buds in the outer skin enter the brain exclusively by the facialis root; those from within the mouth by the facialis, glossopharyngeus and vagus roots, chiefly the latter. A special tuberosity of the brain, the lobus vagi, serves in fishes generally as the primary cerebral center for all gustatory nerves. This is greatly enlarged in some cyprinoids to provide for the taste buds in the palatal organ, and in both cyprinoids and siluroids there is another tuberosity de

veloped, the lobus facialis, which receives all the gustatory nerves from the outer skin.

The purpose of this study is to trace the farther course of these gustatory pathways within the brain and in particular to map out the reflex paths for the various types of gustatory reaction which have been actually observed in the feeding activities of these fishes.

Peripheral gustatory nerve fibers (especially those of the X and IX nerves) enter the brain in company with unspecialized visceral sensory fibers from which they can be distinguished within the brain only with difficulty. This mixed system is spoken of as the communis system of nerves and centers. It is probable that the complete analysis of this complex can be made only by the degeneration method. But the comparative method has enabled us to determine with great probability the chief secondary connections of both types of fibers and so to prepare the way for an accurate determination of the gustatory pathways in the human brain, which are at present almost wholly unknown.

In the cyprinoids and siluroids the primary gustatory centers possess in both the facial and the vagal lobes two types of secondary neurones; (1) small intrinsic neurones (largely of GOLGI'S type II) filling the interior of the lobe, and (2) larger and very highly specialized neurones superficially arranged over the lobes the chief secondary gustatory neurones.

The intrinsic neurones serve to diffuse incoming stimuli throughout the substance of the lobes and those with longer neurites effect connections with adjacent motor areas, chiefly by way of the substantia reticularis grisea. These connections are probably very largely for unspecialized visceral sensory reflexes, as well as for direct response of the mandibular branchial and palatal musculature (muscles of the visceral system) to gustatory stimulation, and are probably substantially similar in all vertebrates.

The chief gustatory neurones of both vagal and facial lobes give rise to the long paths of secondary connection for distant parts of the brain. Their dendrites receive directly the per

ipheral gustatory terminals of the first order and their neurites either descend to the inferior secondary gustatory nucleus in the region of the funicular nuclei or ascend to the superior secondary gustatory nucleus in the isthmus. In both cases the path is mainly and perhaps exclusively gustatory in function.

Fig. 38.

Diagram of the gustatory paths in the brain of the carp as seen from the side. Only the long paths are shown in this diagram (cf. Fig. 39). n. VII.s., n.IX.s., and n.X.s., represent the sensory root fibers of the facialis, glossopharyngeus and vagus respectively, or gustatory neurones of the first order (1). The secondary tracts, both ascending and descending, are marked II. The tertiary path to the inferior lobe is marked III; the path to the cerebellum and valvula, iii. The return path from the inferior lobe to the motor nuclei of the oblongata (tractus lobo-bulbaris) is marked IV. The commissures of the inferior and superior secondary nuclei are indicated by shaded areas (the latter marked c). n.op., the optic nerve. The area marked n.fun. includes the funicular nucleus and the inferior secondary gustatory nucleus.

In cyprinoids the gustatory neurones of the smaller type proba. bly share both this function and that of the intrinsic neurones. In no case does a peripheral gustatory neurone connect directly with a peripheral motor neurone. There is always at least one intermediate neurone between them.

The vagal lobes of the larger cyprinoids differ from those of the siluroids, in addition to the points already mentioned, in the following respects: (1) The chief secondary neurones, being exceedingly numerous and crowded in a narrow peripheral