180 J. B. JOHNSTON, 
VII, IX and X nerves in lower Vertebrates. Osnorn’s fasciculus 
solitarius lies lateral and ventral to the dorsal horn, running parallel 
with the spinal V, which Ossorn recognized, and issues with the 
X nerve. This tract, present in Cryptobranchus, seems not to have 
been found in any other form. It is possible that the secondary 
vagus tract and spinal V are mingled in Cryptobranchus as in some 
fishes (cf. page 165 ff). His fasciculus solitarius ~ corresponds in 
position to the secondary vagus tract in Acipenser and other fishes, 
but his statement that it passes out in the X nerve would seem to 
indicate that he was in reality dealing with the spinal V component 
of the X, now well known in fishes and Amphibia. 
STRONG (95) describes the fasciculus communis in the tadpole 
and homologizes it with the fasciculus solitarius of higher Verte- 
brates and with the lobus vagi of fishes. He failed to recognize 
that the so-called lobus trigemini of Teleosts was a part of this 
system. STRONG at one place considers the supposition that the 
fasciculus communis is to be taken together with the spinal V as 
representing the dorsal horn of the cord, but his description, so far 
as it goes, gives no ground for assuming similarity of structure or 
continuity of tissue between the fasciculus communis and the dorsal 
horn. 
Besides Strone’s work no study of this region has been made 
in the Amphibia by the Gorgı method. I have examined several 
series of Gouar sections of the frog’s brain and find the fasciculus 
communis having the general position and relations figured by STRONG 
(95, tab. 11). It is noteworthy that not only is the fasciculus com- 
munis in the frog surmounted by the acusticum, but the internal — 
arcuate fibres from the acusticum pass mesial to the fasciculus com- 
munis or pierce it. It is this fact that accounts for the gradual re- 
treat of the fasciculus from the central cavity as it runs forward. 
In this respect the fasciculus in Amphibia and in higher Vertebrates 
differs markedly from the lobus vagi of fishes. I have not noticed 
that this difference has been pointed out or commented upon. In 
the fishes, without exception so far as I know, the lobus vagi borders 
directly on the central cavity throughout its whole course, until its 
fibres bend laterad to pass out in the VII nerve. The acusticum 
lies dorso-laterad and the arcuate fibres pass lateral to the lobus 
vagi. The extraordinary change in the relative size of these two 
structures in the Amphibia, as compared with the fishes, has brought 
about a change in relative position as well. In the Amphibia the 
