artery along the neck somewhat superficially, and then continuing for another inch
it terminates in a rete mirahile as on the left side, immediately external and anterior
to the junction of the first sternal rib with the manubrium. There is no defined
axillary, and therefore no brachial artery, properly so called; this latter vessel being
represented by a rete mirabile following the nerve as on the right side. The left
posterior thoracic artery arises about two inches and a quarter from the origin of
the left subclavian artery.
The most remarkable feature of these vessels is the abrupt manner in which
the branches are given off in dense tufts to form a rete mirabile; also the circumstance
that the main arteries, themselves proceeding from the arch of the aorta,
terminate abruptly in a similar rete mirabile.
The preceding description has been taken from a newly dead dolphin, the
vessels of which were carefully injected immediately after death. The parts
about the neck of this Cetacean are usually difficult to demonstrate, as they
very rapidly decay. And even in specimens well preserved in alcohol, and to
all appearance quite unimpaired, I have yet invariably found that decay had
set in at the neck, doubtless from the amount of blood with which this region
is surcharged.
Brain.—Those who have attempted to preserve and examine the cerebral
substance in mass in a hot climate will appreciate the difficulties of so doing. I succeeded
in extracting the brain of one animal, but the fluid in which it was necessary
at once to preserve it so shrunk the organ as to destroy many of its prominent
features (PI. XXX, figs. 1, 2, and 3). I afterwards had recourse to taking an
internal cast of the cranial cavity, which has supplied certain data defective in the
preserved brain. In the following wood-cut (Mg. 16, p. 467) I have given the
outlines of the casts of the brain cavities of Orcella and of Blatamsta, the former
enclosing the latter, both having been drawn to one scale so as to bring out the
differences in form and size of their brains, the two animals from which the casts
were taken having been of similar length.
I shall first describe separately the brain itself with its convolutions, &c., and
then the plaster mould, and lastly draw attention to the distinctions between this
latter and that of Orcella. I t is to be borne in mind that what I state with regard
to the dimensions, &c., of the preserved brain requires to be modified by what obtains
in the cast.
The brain taken from the alcohol had an antero-posterior measurement of 2’90
inches, a transverse diameter of 2'65 inches across the occipito-temporal regions,
though only a width of 2'20 inches at the frontal regions, its greatest vertical height
or depth being 2'10 inches. The cerebellum was a couple of inches broad, an inch
and two-tenths long, and rather less than one inch deep. Not only had the preservation
in spirit diminished: its size as a whole, but the tendency was to give the
brain a more irregular lob-sided appearance than it originally possessed, or than
the mould warranted. Nevertheless, even in the fresh condition, there was an appreciable
difference between the two sides, and, as will be shown, the convolutions of
the right and left hemispheres materially differ. What inequality existed, and
even the defects from unequal contraction, I have had represented, so that the
figures 1, 2, and 3, PI. XXX, faithfully pourtray the object.
The basal surface (Eig. 3) elicitates the peculiarities of the origin of the cranial
nerves. The olfactory bulb does not appear to exist in that area, although the cast
shows a protuberance. The optic commissure is relatively feebly represented,
although its presence in the depression of the lamina cinerea is distinct. What is still
more singular is the extraordinary diminutive pair of optic nerves (5) themselves.
These are scarcely, if at all, thicker than an ordinary sewing thread. Indeed, it
required a close searching observation to detect them, and the greatest care and skill
in manipulation to trace them; for in raising the membranes the chances of breaking
them across were great. But I succeeded in following them up to the very
minute perforations by which they entered and passed through in the skull. To
the optic foramen I shall again refer in my description of the constituent bones of
the cranium.
The pituitary body {%>) is of considerable size ; even after having been preserved
in spirit it retained a comparatively large magnitude. I t is of an elliptical or
transversely oval figure, 0’50 by 0*25 inch in its opposite diameters, and is of a firm
consistence. Two united elevated bodies (a), immediately behind it, appear to be
corpora albicantia. The precise conditions of these and their relations to the third
pair of nerves I could not ascertain; for the membranes and large vascular plexus
interfered With a correet interpretation of the parts; hence, as indistinctness prevailed,
I have omitted in the figure (Mg. 3) the third and fourth pairs of nerves.
In connection with this difficulty of demonstrating the existence of these nerves, it
is interesting to bear in mind that I have ascertained the muscles of the eye-ball
to be only rudimentary.
As to the trifacial or fifth pair of nerves (5), these are very conspicuous; both
fasciculi constituting the roots being easily determinable, and their superficial origin, as
usual, referable to the area of the crus of the cerebellum. The filaments composing
the posterior root are stout coarse and very numerous. About half an inch or
thereabouts from the superficial origin of the nerves is the broad flat and large
Gasserian ganglion, but the branches from it and the further distribution of the
nerves were not pursued.
Close behind the fifth, and therefore possibly a little more laterally than in the
higher mammals, there is a good-sized cord of the sixth nerve (6).
Judging from the origin and relative position, namely, almost abreast of the
sixth nerve, and to the sides apparently joining the pons Varolii to the medulla
oblongata, there springs laterally the enormously large nerve cords of the seventh
pair (7). At the hinder border of each a much thinner nerve is closely applied,
but not quite correctly shown in fig. 3. If this interpretation be correct, and I have
every reason to believe it so, seeing that Tiedemann and others admit there is a
large acoustic nerve in the Dolphin {Delphi/was delphis),—then Platanista agrees
in this particular, and adds one more fact to the general proposition, that the