The position of this area of the carp is indicated in Fig. 22. It is reached, as shown in the figure, by a slender branched process of one of the chief tertiary neurones, which may be a dendrite, but more probably is a collateral neurite, though it does not spring from the main neurite (n), which enters the tertiary tract separately. The neurone marked a lies in the adjacent section and is drawn enlarged in Fig. 25. From the base

Fig. 22. Section taken through the superior secondary gustatory nucleus of the carp. GOLGI method.

X40.

The section is approximately transverse, but strongly inclined so that the dorsal and right sides are father caudad. A single chief tertiary gustatory neurone is shown, whose neurite (n) enters the tertiary gustatory tract. Its main dendrite passes out of the plane of the section (cf. Fig. 25). A much more slender process is completely impregnated, running dorsad and caudad to reach the substantia reticularis grisea trigemini (s.r.g.). At a is shown the position of the neurone drawn in Fig. 25, which lies in the section adjacent to the one here drawn. The secondary gustatory nucleus is bordered on the dorsal and mesial sides by the fibers of the tertiary tract.

of its neurite is given off a collateral, only a part of which is shown, which is probably of the same type as the one here figured. Contiguous sections of the same series show fibers passing from this area of substantia reticularis directly into the axis of the secondary gustatory nucleus and there arborizing, which probably represent dendrites of the cells of the substantia reticularis which are not impregnated.

These fragmentary data are sufficient to show that we have in addition to direct connections of dendrites of the motor V nucleus with secondary gustatory fibers, a similar but indirect functional connection via the substantia reticularis grisea trigemini. The numerous other connections of the latter area need not now concern us.

One of my GOLGI preparations of the carp shows dendrites of a very large neurone lying in the vicinity of the nucleus of origin of the IV nerve sending dendritic branches ventrad into the region caudad of the commissura ansulata and other large branches farther caudad and laterad into the same portion of the secondary gustatory nucleus which is reached by dendrites of the motor V nucleus. The impregnation is so imperfect that it is impossible to be sure whether this neurone belongs to the motor nuclei of the eye muscle nerves or to the fasciculus longitudinalis medialis or to some other neighboring structure.

3. Superior Secondary Nucleus and its Connections.

The superior secondary gustatory nucleus presents, broadly speaking, the same general arrangement as the primary endstation in the vagal and facial lobes. That is, the secondary neurones end in relation with two types of tertiary neurones (1) intrinsic neurones, filling the interior of the nucleus ("Rindenknoten," MAYSER) and (2) the chief tertiary neurones in a dense layer around the periphery. The chief difference between the arrangement of the primary and secondary end-stations. lies in the fact that the latter is connected with its fellow of the opposite side by a broad commissure, the commissure of the secondary vagus nuclei of JOHNSTON. As was recognized by MAYSER, this commissure contains fibers of at least two sorts (1) neurites of the intrinsic tertiary neurones, (2) terminals of a portion of the secondary gustatory tract. From (2) it follows that the secondary tracts end partly on the same side and partly in the secondary nucleus of the opposite side, the former portion being much the larger. The uncrossed portion ends by free arborizations within the secondary nucleus and also extensively in the cortical

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.); l.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