STRUCTURE AND DEVELOPMENT OE LEPIDOSTEUS. 
375 
(No. 15). The figure of the latter author, representing a longitudinal section through 
the brain, is the most satisfactory, the other figures being in many respects inaccurate ; 
but even Wilder’s figure and description, though taken from the fresh object, appears 
to us in some respects inadequate. He offers, moreover, fresh interpi etations of certain 
parts of the brain which we shall discuss in the sequel. 
We have examined two brains which, though extremely soft, were, nevertheless, 
sufficiently well preserved to enable us to study the external form. We have, more¬ 
over, made a complete series of transverse sections through one of the brains, and our 
sections, though utterly valueless from a histological point of view, have thrown some 
light on the topographical anatomy of the brain. 
Plate 25, figs. 47 A, B, and C, represent three views of the brain, viz. : from the side, 
from above, and from below. We will follow 7 in our description the usual division of 
the brain into fore-brain, mid-brain, and hind-brain. 
The fore-brain consists of an anterior portion forming the cerebrum, and a posterior 
portion constituting the thalamencephalon. 
The cerebrum at first sight appears to be composed of (a) a pair of posterior and 
somewhat dorsal lobes, forming what have usually been regarded as the true cerebral 
hemispheres, but called by Wilder the prothalami, and ( b ) a pair of anterior and 
ventral lobes, usually regarded as the olfactory lobes, from which the olfactory nerves 
spring. Mainly from a comparison with our embryonic brains described in the sequel, 
we are inclined to think that the usual interpretations are not wholly correct, but that 
the true olfactory lobes are to be sought form small enlargements (Plate 25, figs. 47 A, 
B, and C, olf.) at the front end of the brain * from which the olfactory nerves spring. 
The cerebrum proper would then consist of a pair of anterior and ventral lobes (ce.), 
and of a pair of posterior lobes (ce'.), both pairs uniting to form a basal portion behind. 
The two pairs of lobes probably correspond with the two parts of the cerebrum of 
the Frog, the anterior of which, like that of Lepidosteus, was held to be the olfactory 
lobe, till Gotte’s researches showed that this view was not tenable. 
i he anterior lobes of the cerebrum have a conical form, tapering anteriorly, and are 
completely separated from each other. The posterior lobes, as is best shown in side views, 
have a semicircular form. Viewed from above they appear as rounded prominences, 
and their dorsal surface is marked by two conspicuous furro ws (Plate 25, fig. 47 B, ce'.), 
which have been noticed by Wilder, and are similar to those present in many Teleostei. 
Their front ends overhang the base of the anterior cerebral lobes. The basal portion of 
the cerebrum is an undivided lobe, the anterior wall of which forms the lamina terminalis. 
What we have above described as the posterior cerebral lobes have been described 
by Wilder as constituting the everted dorsal border of the basal portion of the 
cerebrum. 
The portion of the cerebro-spinal canal within the cerebrum presents certain 
primitive characters, wBich are in some respects dissimilar to those of higher types, 
The homologies of the olfactory lobes throughout the group of Fishes require further investigation. 
MDCCCLXXXII. 3 c 
