MAUTHNER’S CELL 93 
the greatest specialization. According to my interpretation, cer- 
tain cells of the nucleus in the acoustic region are differentiated 
from the rest of the nucleus to form part of a direct, highly 
medullated reflex path from the internal ear and lateral line or- 
gans to the motor nuclei of the swimming muscles; these are 
Mauthner’s cell and the cells which I am homologizing with 
the Miiller’s cells of cyclostomes. 
The nucleus may be roughly divided into three parts, which 
differ somewhat in their connections, though the differences are 
not sharply defined (figs. 1 and 2): (1) The rostral quarter, 
just referred to as the most highly differentiated portion, is re- 
lated chiefly to the acoustico-lateral system and cerebellum and 
consists of four distinct cell groups. (2) An intermediate quar- 
ter (pars intermedia) extends through the greater part of the 
facial lobe and is related to the gustatory VIIth centers, as well 
as to the acoustic nuclei. (3) The caudal half (pars inferior) 
extends somewhat rostral and caudal of the vagal lobe, shows 
less specialization than the rest, and is least influenced by acous- 
tic impulses but more so by impulses from the spinal Vth nucleus 
(fig. 2, S.g.R.) and the Xth nuclei. 
Pars inferior. The caudal half of the nucleus motorius teg- 
menti is practically coextensive with the vagal lobe (fig. 2, 
N.Mot.Teg.inf.). It is less directly connected with the acoustico- 
lateral system than the rest, its cells are smaller, more diffusely 
arranged and in general less highly differentiated. It is very 
like the caudal part of the pars intermedia shown in figure 5. 
The connections of this part of the nucleus are mostly tactile and 
gustatory. The vagal connections have been described by C. J. 
Herrick (’05) and I can confirm his account for Ameiurus. The 
fibers from the nucleus intermedius vagi and the substantia gela- 
tinosa Rolandi pass ventrally as internal arcuates and either 
cross in the ventral commissure or descend in the raphé to enter 
the nucleus motorius tegmenti of the opposite side. Some are 
uncrossed, as are the collaterals from the secondary visceral 
paths. Figure 2 shows the acoustico-lateral nuclei extending to 
the level of the pars inferior and impulses from these nuclei reach 
its rostral end. The efferent fibers of the group are difficult to 
