INIA GEOFFRENSIS AND PONTOPORIA BLAINVILLII. 103 
ally diminishing in size. The mode of attachment of the ribs to the vertebral column 
has been noticed in the description of the thoracic vertebre. 
The extreme length of the ribs of the right side in a straight line is as follows :— 
HEWN tiaectora sani sersiatttacistan NGS acta ate sat ae 6°9 
ICCON Gi etme veces a7 INfiatda’  Sopatteee seen 6:7 
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IRS be dM soceoameneeee tare {a Bleventiaesees pease aes 6:4 
Dua See Ober eee eee 7°33 ‘welit mares sncsteacnas 5°9 
Similbeana casconeetesact 12 Thintecnthiescsssaeeace 53 
SEV Cimudal igeenceceesences Tall 
The costal cartilages, as in Platanista and all the Physeteride, are not ossified. How ~ 
many may have reached the sternum it is, in the present state of the skeleton, impos- 
sible to determine; but indications of the attachment of only two pairs are to be seen 
on this bone, which, if confirmed, would be most exceptional among Cetacea, and be 
another feature of resemblance with the Sirenia. 
The sternum (Pl. XX VII. figs. 5, 4 & 5) is very peculiar in shape, quite unlike that 
of any other Cetacean with which I am acquainted, and in its shortness, breadth, and the 
deep notch on the anterior border somewhat recalling that of the Manatee. It differs 
from this, however, in its greater solidity, especially towards the anterior part, and in 
possessing two strong triangular processes (4) projecting downwards and outwards from 
the fore part of the external surface. 
It consists of a single bone, which is at present but incompletely developed, all the 
prominences and the whole hinder margin terminating in cartilage. 
The extreme length of the ossified portion of this singular bone is 42; its greatest 
breadth, near the middle, is 5". Its general form is irregularly oval. In the anterior 
border is a notch 1” in depth, with smooth, rounded edges. On each side of this are 
two thick conical processes (a), projecting directly forwards, ‘7 apart at their ends. As 
these have dried cartilage both on their tips and inner surfaces, it is possible that in 
the adult animal their ossification might extend so far as to convert the notch into a 
foramen. On each. side of the hinder half of the notch the bone becomes very thick, 
running out on the external or inferior surface into the triangular process before no- 
ticed (4), and backwards and upwards into a thick irregular edge (c), apparently for 
the attachment of the cartilage of the first rib. The hinder half of the bone is flat, 
and gradually becomes thinner towards its rounded and incomplete posterior edge, which 
is divided into two lobes by a narrow cleft, situated slightly to the right of the median 
line. About the middle of the left lateral margin is a small transverse notch, re- 
presented on the right side by an oblique perforation, apparently for the passage of a 
blood-vessel. Immediately behind this the margin is thickened and excavated for the 
attachment of the cartilage of the second pair of ribs (d). There are no other indica- 
VOL. VI.—PART IIL. Q 
