both the peripheral and the central gustatory paths in all vertebrate types and that fishes like the carp with enormous hypertrophy of the gustatory roots of the VII, IX and X nerves may safely be used as guides to point the way for further researches upon the gustatory paths of higher vertebrates where the system is less easily analyzed. Such being the case, our problem assumes a measure of importance when we remember that the central gustatory pathway is at present almost totally unknown in all vertebrates, including man, and that even the peripheral pathway is still in dispute among students of human anatomy.

It has been already pointed out (JUDSON HERRICK, '04) that the siluroids (cat fishes and horned pouts) and the larger cyprinoids (carps, suckers, etc.) present a striking similarity to each other and contrast to other teleosts in both the peripheral and the central nervous systems, and that these features center about the gustatory pathways. In teleosts generally the gustatory pathway from the lining of the mouth in the branchial region, entering the brain by the communis roots of the IX and X nerves, and the gustatory pathway from the anterior part of the mouth and from the outer skin, entering by the communis VII root, terminate together in a single cerebral enlargement, the lobus vagi. But in these two groups of fishes we have a second tuberosity, as mentioned above, developed for the communis root of the facialis to provide for the unusually large number of taste buds in the outer skin supplied by this nerve.

In the cyprinoids, particularly the carp-like forms, both of these lobes are enlarged, correlated with a high development of the taste buds in each of the corresponding peripheral regions, but particularly in the vagal region to supply the remarkable collection of taste buds on the palatal organ. In the siluroids, on the other hand, there is no hypertrophy of the gustatory organs in the branchial region and the vagal lobes, accordingly, are essentially similar to those of other teleosts. But the highly developed cutaneous gustatory organs innervated by the facialis have called forth an enlargement of the facial lobe greater than that of cyprinoids. Since in the siluroids all of the taste buds of the outer skin are supplied by the communis root of the

facialis (JUDSON HERRICK, 'OI) and since the palatal and other branches of the communis VII root which supply taste buds within the mouth are not enlarged, as compared with other fishes, it is clear that the enormous communis VII root and the lobus facialis in which it terminates are related mainly to cutaneous taste buds in these fishes.

Fig. 4. Dorsal view of the brain of the yellow cat fish, Leptops olivaris (Raf.), X 2.

The olfactory bulbs are cut off; also the membranous roof of the fourth ventricle, exposing the facial lobes (L. F.) and vagal lobes (L. V.). This ventricle is bounded behind by a transverse ridge containing the commissura infima HALLERI (c. i.) and the commissural nucleus of CAJAL. The tuberosity laterally of the cerebellum and facial lobe is the lobus lineae lateralis (7. 7. 7.), which is greatly enlarged and entirely conceals the superior secondary gustatory nucleus.

SECTION III. THE CENTRAL GUSTATORY SYSTEM OF CYPRINOID FISHES.

We shall now proceed with a description of the gustatory pathways in a selected series of teleosts, beginning with the larger cyprinoids where it attains its maximum development. The results here obtained will be controlled by an equally careful examination of the brains of siluroid fishes (particularly Ameiurus), whose gustatory centers differ greatly in detail from those of the carp-like forms. These minor differences will serve to bring out more clearly the points of fundamental resemblance, which are very striking.

The end-station of the gustatory neurones of the first order (peripheral neurones) is the nucleus of origin for the neurones of the second order, giving rise to secondary gustatory tracts, and these in turn to tertiary tracts. The nomenclature of these tracts and centers offers almost insuperable difficulties and some new terms will have to be introduced and old ones more nar

rowly defined. A summary of the nomenclature here employed for the gustatory system of these fishes is given in tabular form in Section V, to which frequent reference should be made.

I. Primary Gustatory Centers.

The general topography for the vagal and facial lobes of cyprinoid fishes has often been described, and the reader is referred for the details to the classic paper of MAYSER ('82), and also to the figures of BELA HALLER ('96), whose descriptions, however, I do not in all things confirm. I have found little in the extensive work of this author ('98) on the brains of Salmo and Scyllium which sheds further light on the secondary connections of the vagal lobe. However, I do not profess to have mastered the contents of this unsystematic and obscure paper, though I have dilligently studied it. Nor is there anything of importance from our present point of view in the recent dissertation on the vagal lobes of cyprinoids by GROTH ('00), whose purpose was merely to test the accuracy of some of HALLer's observations on nerve anastomoses in these fishes.

The vagal lobe of the cyprinoids, as compared with that of the siluroids and the teleosts generally, represents an enlargement of both the sensory and the motor centers of the vagus and glossopharyngeus. This enlargement is correlated with the development of the curious palatal organ in the mouth of these fishes, the sensory fibers being derived from the taste buds which cover the surface of this organ and the motor fibers going out chiefly to the small muscles which permeate its interior. The "motor layer" of the vagal lobe, from which these motor fibers are derived is a dorsal extension of the nucleus ambiguus. The latter nucleus has the typical position and relations, supplying the branchial musculature, and is not commonly regarded as a part of the vagal lobe.

We shall describe, so far as the material at command permits, the conduction pathways in the vagal lobe of the larger cyprinoids on the basis of sections of adult and young brains. cut in various planes and stained by DELAFIELD's haematoxylin and the methods of WEIGERT-PAL and GOLGI. The illustrations

given throughout the remainder of this paper are all camera drawings of single sections, except Fig. 20, which is a composite, and the schemata, Figs. 38, 39 and 40.

The

First a few words by way of general orientation. vagal and facial lobes are dorsal structures in the oblongata, but they do not represent, as commonly taught, the morphological continuation of the dorsal horns of the spinal cord. These are represented in, the spinal V tract and its associated substantia gelatinosa Rolandi, their ventro-lateral position in the vagus region of these brains being due to crowding by the more mesially placed gustatory centers. The latter centers, therefore, if morphologically related to anything in the spinal cord, must represent spinal structures lying dorsally of the canalis centralis and beneath the floor of the dorsal fissure. In the oblongata this fissure opens out and its floor becomes greatly extended to form the membranous roof plate (His), or velum medullare posterior, beneath which the lobes in question are developed (cf. JUDSON HERRICK, '99, p. 213).

Figure 5, taken midway of the vagal and facial lobes of the carp, illustrates how these structures are superposed upon the great longitudinal conduction paths which constitute the chief landmarks of morphological relationship. The spinal V tract, whose substantia gelatinosa at this level is reduced to a mere vestige, lies ventrally of both the sensory and motor vagus roots. Crowded into the space ordinarily occupied by the substantia gelatinosa Rolandi are the great longitudinal secondary gustatory paths, ascending and descending. Mesially of these is the substantia reticularis, shown by CAJAL and others to be the continuation of the ventro-lateral funicle of the spinal cord and to be composed of short paths, mostly sensory fibers of the

Fig. 5. A transverse section taken through the middle of the vagal and facial lobes of an adult carp stained by the method of WEIGERT-PAL. X 16.

The layers of the facial lobes and the vagus roots are designated at the right. a. s. X., ascending secondary gustatory tract from the vagal lobe; com. r. VII, communis (gustatory) root of the facialis entering the facial lobe; d. s. VII, descending secondary gustatory tract from the facial lobe; Im., lemniscus (laterales Längsbündel, MAYSER); sp. V. spinal root of the trigeminus.