No. 1.] AMPHIBIAN BRAIN STUDIES. 71 
GENERAL CONCLUSIONS. 
A general survey of the distribution of the nuclei, shown in 
Fig. 21, as described in the preceding sections, points to the 
natural division of the cranial nerves into three groups: Group 
A embraces the Vagus, Glossopharyngeus, Facialis, and Trige- 
minus. Group B embraces the Abducens, Trochlearis, and 
Oculo-motorius. Group C embraces the Acusticus. 
The known tracts and nuclei possessed in common by each of 
these groups are distributed below : — 
Group A. Group B. Group C, 
X.-IX., VIL.-V. VI., IV., IH. VIII. 
1. Dorsal! sensory nuclei 1. Special ventral motor 1. Special sensory nuclei. 
(? wanting in the roth). nuclei. 2. (Fasciculus communis 
2. Lateral motor nuclei 2. Posterior longitudinal from sensory nuclei ?.) 
(? wanting in the roth). fasciculus. 3. Posterior longitudinal 
3. Fasciculus communis? fasciculus. 
from sensory nuclei 
(not observed in the 
5th). 
4. Ventral! motor nuclei 
(wanting in the 7th). 
The nerves of Group A are apparently closely homologous, in 
so far as their mode of origin is concerned. The dorsal sen- 
sory nucleus of the t1oth, 9th, 7th, and 5th pairs shows the 
most marked continuity, and the nerve bundles are seen to issue 
directly from it. The ventral motor nuclei of the 9th and 
and roth (10 z and 9 z') are continuous, and occupy the same 
region as the great ventral motor nucleus of the 5th. The fas- 
ciculus communis, first appearing in the posterior horn, and 
all along in close contact with a small group of sensory cells, is 
given off to the 10th, gth, probably to the 7th, and possibly to 
the 5th. The lateral motor nucleus, consisting of the 
cells in the angle of the medulla, contributes to the goth, 7th, 
and probably to the 5th. 
The absence of the ventral motor nucleus from the 7th nerve, 
and the large motor element in the 5th, may indicate that some 
1 These adjectives, dorsal and ventral, are retained, since these nuclei are simply 
thrust laterad by the opening of the 4th ventricle. 
2 This is upon the probability considered on p. 00, that the fasciculus com- 
munis joins the 7th instead of the 8th. 
