yt H. W. NORRIS 
‘Cas the bundle ascends in the cerebellum it gives off two bundles, 
one near the base of the tectum and the other near the dorsal 
surface.”’ In Siren the lateral fine-fibered part of the radix di- 
vides into two portions at its separation from the medial coarser 
fibered part, one of these divisions passing into close relation with 
the cerebellar fiber tract as above stated, the other extending into 
the tectum more directly and ventrally. In Siren as in Necturus 
‘“the mesial bundle is larger and contains the coarser fibers. It 
continues forward and upward into the cellular zone of the tectum 
in which the fibers spread widely and soon lose their sheaths’’ 
(fiz. 20, Vrim.). 
The figure given by Johnston (’06, p. 246, fig. 125) of a cross- 
section of the brain of Necturus through the cerebellum, in which 
the decussatio veli occurs in the tectum opticum, entirely distinct 
from the cerebellar commissure, calls for some comment. As 
far as the writer can learn no such condition is reported for any 
other Amphibian. A slender band of fibers, constituting a dorsal 
commissure extending across at the posterior border of the velum 
medullare anterius, and with which is closely associated the de- 
cussation of the trochlear nerve, is characteristic of the Amphibia, 
and commonly known as the ‘decussatio veli.’ As to the nature 
of the commissure there is difference of opinion. It has been 
generally considered a part of the cerebellum; in fact it is always 
associated with the latter in whatever degree the latter is devel- 
oped. Bindewald (11) states that, in the absence of a cerebellum 
in Proteus and Hypogeophis, this commissure is wholly concerned 
with the terminal nuclei of the sensory part of the trigeminal 
nerve, and he terms it ‘commissura intertrigemina.’ He asserts 
that in other Amphibia, while the presence of a cerebellum may 
involve other fiber constituents in the commissure, the latter 
is primarily not a cerebellar commissure. According to Johnston 
(06, p. 229) the decussatio veli (of Selachians) is a commissure 
between the secondary gustatory sensory nuclei. In the figure 
of a cross-section of the brain of Necturus, referred to above, 
Johnston represents the decussatio veli passing, not through the 
velum, but through the tectum and connecting the secondary 
gustatory nuclei. But the cerebellar commissure is represented 
