INIA GEOFFRENSIS AND PONTOPORIA BLAINVILLII. 101 
an extraordinary deviation from all other Cetaceans, among which the number, though 
certainly very variable, is usually considerable, ranging from eight in Platanista and 
Physeter to twenty-four in some of the Delphini and Lagenorhynchi. On the other 
hand, in the Sirenia, the lumbar region of the vertebral column is, as in Jnia, extremely 
restricted. 
The three lumbar vertebre are very remarkable for the great antero-posterior 
breadth of their processes, both spinous and transverse. The bodies are large, being 
respectively 1:3”, 1:4", and 1:5" in length; their extremities are subcircular, and, as 
usual in the Cetacea, the middle of the side below the origin of the transverse process 
is much contracted, so that the median line of the under surface forms a sharp ridge, 
from which a strongly marked arterial groove runs outwards and backwards to the 
hinder edge of the root of the transverse process. The spinous processes resemble 
those of the posterior dorsal region; the first two are slightly curved forwards, the last 
is nearly vertical and somewhat smaller. The oblique processes (metapophyses) are 
short, flat, rounded projections from the upper part of the lamine of the arch, very 
closely approximated to each other. The transverse processes rise from the whole 
length of the side of the body; they are of nearly equal length, but increase in breadth, 
especially by the development of a considerable angular process on the middle of their 
anterior border, most conspicuous in the third vertebra; beyond this process the 
anterior border is sharply cut off, so that the extremity appears to point backwards. 
The hinder border is nearly straight, with a notch close to its origin from the body, 
continuous with the groove before spoken of on the inferior surface of the bone. 
The vertebra here reckoned as the first caudal closely resembles the last lumbar. 
Its body is of the same length, but its transverse process is even broader. The suc- 
ceeding tail-vertebre keep up the same general character, having large heavy bodies 
and broad processes. The projecting surfaces on the hinder edges for the attachment 
of the chevron bones are very strongly marked as far as the ninth, after which they 
become obscure; they are not seen on the anterior edge until the fifth. It is difficult 
to determine exactly how many chevron bones there were, but probably not more 
than eleven. ‘The spinous processes, broad and rounded at their summits, become 
gradually lower, until in the tenth the greatly reduced vertebral canal is scarcely closed 
in by the lamine of the neural arch, and there is no longer a true spine. In the 
eleventh, the canal is altogether open above. The metapophyses continue in much the 
same relative development and situation as far backward as the spinous processes 
extend. The transverse processes gradually diminish in length, and lose their charac- 
teristic form. Already in the second that cutting away of the anterior edge noticed in 
the lumbar region is lost; and in the third and succeeding vertebre the anterior edge is 
straight, and the hinder one sloping, so that they appear to point forwards. In the 
eighth they form but a slight prominence on the anterior part of the body, and in the 
ninth they have altogether disappeared. The vertical perforations for the lateral 
