I have hitherto said little respecting the lobes, these being, in fact, very much out
of position compared with the mould of the brain. A frontal, parietal, occipital
and temporal are undoubtedly present and well marked, but regarding the so-named
middle or central lobe of Gratiolet I hesitate to affirm anything.
On making a median longitudinal section of the brain, and thus exposing the
inner cerebral face, I noted among others the following points : the great and preponderant
volume of the occipital lobe; the very considerable depth of cerebral
substance above the corpus callosum, &c. ; an unusual arching of the corpus
callosum of moderate thickness at its middle, but with greatly increased thickness
of the anterior genu, and specially knob-like posterior spherical extremity; some
depth of the fornix behind, but thinning forwards; the thalamus opticus of
relatively small, or rather moderate dimension ; and prominent corpora quadri-
gemina.
As to the convolutions and sulci of this inner face, the callosal gyrus makes
one great sweep from behind forwards, ' broadening as it proceeds, and at its sharp
turn in front being twice as wide as it is behind. I t has no folds in its entire
course. The calloso-marginal gyrus is like the last and surrounds it ; having only
one oblique antero-posterior indentation at the frontal region where it is, so to
say, cleft.
The lateral ventricles are short. The termination of the anterior cornu is
blunt and barely directed outwards, but, on the contrary, the cavity trends inwards
and is deep ; the corpus striatum being large, and markedly vertically directed. The
posterior cornu likewise is abbreviated so far as its sweep back and inward bend
extend, but it is nevertheless deep, and there is a rudimentary hippocampus minor,
agreeing with the small calcarine gyrus of the inner cerebral face. The middle
cornu also strikes very nearly straight downwards, and it possesses a distinct
hippocampus major.
Views of the third and fourth ventricles were but imperfectly seen owing to
the above sections destroying the relations of the parts.
The cerebellum is of considerable volume proportionally to the cerebrum,
although, all in all, less than obtains in Orcella. Its superior vermiform process
is narrow, not very prominent, but distinct. Lateral lobes are well marked, but thé
flocculus is only of medium size.
The pons Varolii {Pv) is short in both diameters, but it is thickish. As previously
stated, corpora trapezoidea are attached to the medulla oblongata ; the latter
has no very marked columns, but its smoothness inferiorly may have been produced
by the spirituous medium in which it was preserved.
The grey matter both of the cerebrum and cerebellum is proportionately in a
thick layer, and the sulci, as a rule, in both, açe relatively deep.
Lastly, I would note that the vascular supply to the brain must be great if
we judge by the membranes within and at its base.
All things considered, the brain of Platanista is wanting in the broad rotundity
of the Whale group generally and so marked in Orcella. To a very limited
degree it has Elephantine characters, viz., height and moderate breadth, though one
cannot regard it in any other light than that of a modified Cetacean form.
Fig. 16.
Outlines of the casts of the cranial cavities of Orcella and Platanista, the latter the internal, and the former th
external, outline: drawn to one scale.
Mould of cranial cavity.—The admeasurements of the mould of the cranial
cavity of the adult are as follows:—
' - Inches.
Greatest antero-posterior length (prominence o f frontal lohe to postcerehellar prominence) . 3 26
Greatest hreadth (viz., temporo-oceipital region) . . . • • • • . . 3 65
Diameter at the middle of frontal region, in front of Sylvian depression . • • . 2 80
Greatest height (fronto-parietal region) . . . 3 0 0
Extreme length of each cerebral hemisphere . ’ •' •" ^ ^
Cerebellum in antero-posterior diameter about . ^ §J?-
Cerebellar extreme breadth about ............................................................... • • ’ • 2 20
Vertical height of cerebellum, including the pons Varolii ■ • • . , » 1 8 0
The top view of this cast shows at a glance what is even in some degree apparent
in the shrunken brain, and which the second and third measurements above amply
substantiate, viz., the marked difference in width between the fore and after parts of
the cerebrum, that is to say that, while, as a whole, the brain of Platanista is broad
to its length, the great preponderance of breadth is at the occipito-temporal lobes;
whereas the frontal width is in. reality moderate. Erom above, this cast also shows
two nipple-like projections in the position of the olfactory lobes, but dependent rather
on ethmoidal depressions than on absolute olfactory nervous expansion. The considerable
exposure of the cerebellum is verified in this view of the cast; and the
lofty hemispheres of the cerebrum, the deep valley of the longitudinal fissure and
especially the open angle of the posterior and inner cerebral angles are all
characteristic features.
In the anterior face, the orbito-frontal regions stand forward, whereas the
suprafrontal areas retire. The lower latero-frontal eminences again are distinctly
impressed, compared with the occipito-temporal prominences; these latter in this
foreshortened view standing out almost like wings to the former.
The profile is exceedingly characteristic, for the exceeding loftiness of the
cerebrum, compared to its length, strikes pne as something most unusual. The very
different sweep of the sharply rounded occipital border to the top of the brain, as