8 F. L. LANDACRE 
The anterior end of the metencephalon (figs. 6 and 7) consists 
of two lateral lobes with thick dorsal and ventral walls but with 
thin lateral walls. These, as mentioned above, are overhung by 
the broad flat mesencephalon. The anterior ends of these lobes 
are almost in contact with the posterior ends of the optic vesicles 
(fig. 1). At a point dorsal to the posterior end of the hypophysis 
they fuse on the median line and at a level with the entrance of 
the root of the Gasserian ganglion their cavities become conflu- 
ent with the median ventricle. The roof of these vesicles is 
thick from their anterior end to a point just posterior to the pos- 
terior end of the mesencephalon. These two thick walled vesi- 
cles I take to be the lateral lobes of the cerebellum and the 
thickened roof of the anterior end of the metencephalon, lying 
under the posterior end of the mesencephalon and above the 
unpaired ventricle of the brain, the middle lobe of the cerebellum 
(valvula cerebelli). From the posterior end of the mesencephalon 
the roof of the metencephalon has the usual character of the 
medulla. 
THE GANGLIA AND NERVES OF THE 10 MM. EMBRYO 
Since the components of the cranial nerves in the adult 
Lepidosteus have not been worked out, certain difficulties pre- 
sent themselves when one attempts to identify the ganglia and 
nerves of the 10 mm. embryo. Some of these difficulties will 
appear in the description. For the most part, however, the iden- 
tification of ganglia and nerves and even the identification of 
the components can be made with ease, owing to the isolated 
position of the ganglia and the solitary course pursued by com- 
ponents which are later combined into mixed nerve trunks. In 
the main, the position of definite ganglia is remarkably constant 
among the Ichthyopsida. The most striking differences among 
ganglia are three: (1) the presence or absence of the profundus 
ganglion; (2) the position of the ventro-lateral lateralis of the 
VII; and (3) the extent to which the branchial ganglia of the 
vagus are distinct. The profundus is present in Lepidosteus. 
