arches are ossified to the tenth caudal, and they becoma more and more faint as they
are traced backwards. In the first five they consist of little more than flattened
laminae with a slight projection (metapophyses) on the middle of the anterior
borders, while in the remaining five segments they are reduced to small round
ossicles. In the older specimen the transverse processes have not united with the
centra as far hack as the sixth, their sutures being quite intact; hut in the seventh
and succeeding vertebrae the transverse processes are exogenous products of the
centrum, occupying the position of the autogenous transverse processes, hut chiefly
developed from the anterior portion of the lateral surface of the centra. The neurocentral
suture in the same skeleton is intact to the seventh caudal, but is completely
anchylosed in the succeeding vertebrae.
In the cervical and dorsal regions of the youngest specimen, the epiphyses of
the centra are partially developed, hut in the second example they have nearly
all attained their proportional size to their individual centra.
In a young male with a vertebral column 2 feet 4*70 inches in length, there
are in all twenty-three chevron hones, of which ten are wholly and three partially
ossified, the remaining ten being cartilaginous. The first two are in separate pieces, one
on either side, and the most anterior pair are much smaller than those behind them,
and are only partially ossified and unsymmetrical, the half of the right side being
a mere ossicle imbedded in cartilage, while that of the left side is little developed.
The second hone consists of two wholly ossified halves. The chevron bones from the
third to the eighth inclusive form perfect arches, being united wholly by cartilage,
and are perfectly ossified. The first chevron hone is placed between the twenty-sixth
and twenty-seventh vertebrae, there being in all fifty-one vertebrae in the skeleton.
Ossification o f sternum.—In the youngest specimen, the prestemum consists
of two large ossicles, perfect externally but separated from each other by a wide
cartilaginous interspace, and behind the left ossicle there is another and much
smaller ossicle, before the attachments of the second ribs of either side, In
whatever way this abnormality may he viewed, it would- appear that the two
halves of the prestemum may be occasionally formed, one or both, from more than
one centre of ossification; because the little ossicle in question, being placed
completely anterior to the second rib, would have, in all probability, united with
the prestemum. The anterior angle for the articulation of the first rib is cartilaginous.
In the second specimen, the two halves all hut meet in the middle line,
hut they are not united; and anterior and posterior to this point their inner borders
diverge from each other, most so in the latter direction. Their anterior angles are
perfectly ossified, hut they do not bear the first rib, which is applied to their external
lateral margins. In one individual not more than, if so much as, a month old, the
two halves of the sternum are completely anchylosed, so that it is probable the pre-
stemal elements become almost, if not entirely, united m utero. This specimen
has its anterior half relatively more expanded than in the adult, whereas the specimen
with the first rib attached to its side would doubtless have in adult age a very much
greater breadth at its middle than in a normal sternum.
In the first specimen, no ossicles of the first segment of the mesostemum
are developed, but in the second and third specimens, the ossicle on the left half is
enormously larger than the minute ossicle that lies imbedded in the right half of the
cartilage.
There are distinct indications, on the latter aspect of the mesial sutural line,
of the two original elements. The facet for the first rib is borne on a slight
projection on the anterior angles and looks backwards and outwards. I t is subject,
however, to considerable variation. In one specimen the anterior border is nearly
straight instead of concave.
Conclusion.—In bringing this Memoir to a close, I shall briefly summarize
the more prominent features of the animal of which it treats. The external
characters may be re-iterated thus : a long compressed snout, with a formidable array
of teeth; a vaulted compressed forehead; longitudinal blow-hole; scarcely perceptible
eye; distinct neck; broad and abruptly truncated pectoral fins and small dorsal
fin; and the male, a smaller hut heavier-built animal than the female, with a
shorter snout. To these may he added the remarkable changes which take place
in the teeth and in the curvature of the snout between youth and age.
The most noteworthy peculiarities in the internal structure of this Cetacean
appear to he, the great development of the Eustachian tube and of the large
sacs connected with it, and which lie along the hyoid apparatus; the remarkable
valvular and glandular structure of these sacs, and of their ramifications, only
separated from each other in the mesial line by a thin membrane; the existence of
a peculiar glandular area in the second cavity of the stomach, associated with
enigmatical cup-shaped bodies; the apparent natural shedding of the superficial
membrane of the first gastric cavity as in some birds; the chambered character of
the small intestine, due to the great development of valvulse conniventes; the
existence of a caecum, with which is associated a large gland; remarkable dilatations
in the vascular system of the spleen; the modifications of the spiracular sacs connected
with the blow-hole; the fibrous blubber of the forehead; the modifications
of the laryngeal cartilage; the hroken-up character of the rings of the trachea;
the broad bifid heart; the abrupt termination in rete mirabile of the branches
of the great arteries towards the head, and the anterior extremities; the simply
formed brain, distinguished by moderate breadth and considerable height; the
excessively rudimentary character of the optic nerves; the possible absence of
the third and fourth pairs of cranial nerves; the eye devoid of a crystalline lens
and only a rudimentary choroid membrane present; the rudimentary development
of the-muscles of the eyeball; the glandular character of the conjunctival
covering of the cornea; the presence of utricular-like glands in the vagina
of the gravid female, and the existence of utricular glands in the uterus of the
foetus.W
ith regard to the skeleton, the great development of the maxillary crests;
the anterior compression and elongation of the maxillaries with the premaxillaries;
the prolonged mandible, with its extended symphysis; the position of the palatine in