portion among the chief tertiary cells (Fig. 23). The details of the endings of the crossed fibers I have not been able to observe, but there is every reason to believe that they are essentially similar.

I have no complete impregnations of the intrinsic commissural neurones. The evidence is that their delicate, feebly medullated neurites gather in the interior of the nucleus and terminate after crossing among the dendrites of the chief tertiary neurones of the opposite side. The layer of these chief cells envelopes the secondary nucleus on all sides except where it is interrupted by the secondary and commissural tracts. The neurites of these cells pass directly outward and become medullated as they enter the chief tertiary tract for the inferior lobe. Just external to the layer of tertiary neurones the gustatory nucleus is encapsuled by a dense layer of heavily medullated nerve fibers. These are partly the tertiary fibers, but chiefly cerebellar tracts. The position of the secondary gustatory nucleus in the isthmus is such that the cerebellar penduncles, passing downward from the cerebellum and valvula, almost entirely envelop it. It is this peculiarity which suggested to MAYSER the name "Rindenknoten." Surrounding this fibrous capsule is an aggregate of nuclei with very diverse connections to which MAYSER applied STIEDA's name, "Uebergangsganglion."

This region is perhaps the most intricate and difficult of analysis in the teleostean brain, as it contains several large centers and numerous important tracts, both medullated and unmedullated, all crowded into a very small space. The dorsal part of the isthmus is more than usually crowded in these types, not only by these great gustatory centers, but also by the enlarged cerebellum and valvula and their associated tracts.

The broad line of fusion of the valvula cerebelli with the torus semicircularis (colliculus) is occupied by a very dense mass of cells and medullated and unmedullated tracts whose relations are only imperfectly shown in my preparations. The whole complex, which lies mesially of the nucleus lateralis mesencephali (EDINGER), or colliculus, I term provisionally the nucleus lateralis valvulae.

It is, apparently, the most cephalic

part of the "Uebergangsganglion" of STIEDA. This group of cells fuses behind with the dorsal and cephalic border of the secondary gustatory nucleus, but is separated from it more or less definitely by the medullated vertical cerebellar tracts which encapsule the secondary gustatory nucleus. Sections stained by the method of PAL show large tracts of fine fibers with ex

Fig. 23. Portion of sagittal section of the brain of a young carp, 5 cm. long. GOLGI method. X 40.

The ventral side of the preparation is below and the cephalic end at the left. The section includes the superior secondary gustatory nucleus (“Rindenknoten,” MAYSER) and shows the origin and course of the tertiary path to the inferior lobe. A single neurone of the latter type is impregnated completely (a) save for the terminal arborization. Mingled with the neurites of these cells are those of the tract between the cerebellum and the inferior lobe (tractus lobo-cerebellaris, EDINGER). Among the terminals of the tertiary tract are the cells of origin of the tractus lobo-bulbaris et spinalis (tr.l.b.); 1.m., lemniscus ; tr.t.l., tractus tectolobaris; tr.t.s., tractus tecto-spinalis.

ceedingly delicate medullary sheaths passing dorso-ventrally between the n. lateralis valvulae and the cerebellum and valvula (Fig. 24), and GOLGI Sections show diffuse unmedullated tracts taking the same courses (Fig. 20). Whether the medullated and the unmedullated fibers spring from neurones of the same type, I have not been able to determine. The neurones shown

Fig. 24. Transection through the brain of a large carp just cephalad of the superior secondary gustatory nucleus. Stained by the method of WEIGERT-PAL. X 20.

The section passes through the most cephalic portion of the commissure of the secondary gustatory nuclei, and illustrates the relations of the nucleus lateralis valvulae to this nucleus and to the cerebellum. The trochlearis (n.IV.) decussates just cephalad of the gustatory commissure and in passing to its super

by the GOLGI Sections are like the cells of the granular layer of the cerebellum and probably are of that type, receiving afferent cerebellar impulses and transmitting them to the cortex cerebelli. Whether they receive their impulses from the adjacent gustatory nucleus or from other sources, my preparations do not show with certainty, but probably partly from the former.

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There is also a broad unmedullated connection between the ventral part of the secondary gustatory nucleus and the cephalic part of the n. lateralis valvulae, running cephalad through the vertical cerebellar tracts (designated by b in Fig. 20). Horizontal sections of the brain of Catastomus show numerous delicately medullated fibers running between the whole cephalic face of the gustatory nucleus and the n. lateralis valvulae. These connections lend further support to the belief that the n. lateralis valvulae is in part a gustatory intermediary station for the cerebellum. This nucleus extends cephalad to the point where the valvula severs connection with the floor of the mesencephalon and here a large tract passes between its cephalic end and the nuclei of the third nerve and of the fasciculus longitudinalis which lie mesially of it. It is no doubt this connection which led B. HALLER to state ('98, p. 522) that the "Uebergangsganglion of FRITSCH and MAYSER is an "upper motor oculomotorius nucleus." The nucleus lateralis valvulae

ficial origin become embedded in the most cephalic part of the secondary gustatory nucleus, the latter being represented in the figure by the neuropil surrounding n.IV. Sections immediately caudad show the gustatory nucleus occupying the entire space from near the median line to the lateral surface of the brain and from the level of the commissural fibers and tr. lobo-bulbaris (tr.l.b.) up to the valvula cerebelli.

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cb., cb'., cb2., cb3., cerebellar tracts; com.s.g.n., commissure of the secondary gustatory nuclei; f.l.m., fasciculus longitudinalis medialis; g.III, fibers arising from the granule cells of the nucleus lateralis valvulae and passing dorsally into the lateral lobe of the valvula cerebelli; g.3., tertiary gustatory tract for the inferior lobe appearing as oval bundles among the strands of the cerebellar tract cb.; Im., lemniscus (fasciculus lateralis); n.IV., root of the fourth nerve; n.l.m., the extreme caudal end of the nucleus lateralis mesencephali (torus semicircularis, colliculus); n.l.v., nucleus lateralis valvulae; s., a large blood sinus between the lateral lobes of the valvula; tect.opt., tectum opticum; tr.l.b., tractus lobo-bulbaris; tr.t.b.c., tractus tecto-bulbaris et spinalis cruciatus; tr.t.b.r., tractus tecto-bulbaris et spinalis rectus.

has other connections (with the substantia reticularis of the oblongata, optic thalamus, etc.) which I have not yet fully worked out. Its homologies are discussed briefly beyond. Another part of the "Uebergangsganglion" which serves as a gustatory reflex center is the nucleus already designated as substantia reticularis grisea trigemini. There remain several considerable collections of cells in the "Uebergangsganglion" which may have gustatory functions, but their discussion would involve a more extensive analysis of the mesencephalon than we can here attempt.

A typical illustration of the chief tertiary gustatory neu rones in the cortex of the secondary gustatory center of the carp is seen in Fig. 25. The dendrite plunges into the axial portion of the nucleus ("Rindenknoton," MAYSER) and there spreads out widely among the termini of the secondary gustatory fibers (cf. Figs 22, 23). The neurite passes downward to enter at once the tertiary gustatory tract for the inferior lobe of the same side, where it takes up a dense medullary sheath and so is rarely completely impregnated in GOLGI preparations. These medullated fibers mingle immediately with similar ones of the cerebellar tracts (lobo-cerebellaris and others) which encapsule the secondary nucleus and which likewise pass into the inferior lobe, so that I have found it impossible in WEIGERT sections to effect the separation of the two classes of fibers except at the origin of the tertiary gustatory tract from its nucleus. I have, fortunately, secured a sufficient number of complete GOLGI impregnations to show the origin of the tract without uncertainty. Its entire extent save the terminal arborization is shown in Fig. 23.

The combined tract passes ventrad and somewhat cephalad to enter the caudal border of the inferior lobe and spread throughout the whole of the lateral lobule of this organ. Whether any of these fibers reach the median lobule my preparations do not definitely determine, but apparently not. (The terms lateral and median lobules are used in the sense defined by DAVID (92). The lateral lobules are the hypoaria and the median lobules the mammillary bodies of C. L. HERRICK ('92) ).