INIA GEOFFRENSIS AND PONTOPORIA BLAINVILLII. 99 
body of the last dorsal vertebra is arrived at by a gradual lowering of the transverse process 
of the arch of the first; in the second it is a new process, first appearing on the body 
rather abruptly, as the process on the arch ceases, but for the space of two or three verte- 
bre coexisting with it, as in the cervical region: or, to explain the case in other words, 
the anterior ribs in both have an upper and a lower connexion with the vertebre ; in the 
first instance they lose their lower connexion by the non-development of their neck and 
head, but the gradual lowering of the transverse process brings the headless rib again 
in connexion with the body, by the intervention of a long straight process; in the 
second instance they always retain their lower connexion, but the development of 
a process out of the articular surface of the body, with concurrent shortening of the 
neck of the rib, and disappearance of the upper process of the vertebra, produces an 
exactly similar result. 
In Jnia the mode of attachment of the ribs is, as far as I know, peculiar among 
Cetaceans, being intermediate between the two distinct forms above described, and far 
more resembling that which obtains in the Sirenia and the terrestrial mammals. The 
anterior vertebra have as usual a tolerably well-developed, thick and rounded transverse 
process, springing from the arch at the junction of the pedicle with the lamina, and 
pointing upwards and forwards, with a large articular facet at its extremity; this process 
gradually becomes shorter, till in the seventh vertebra little more than the articular 
facet remains on the side of the arch. On each side of the body of the first vertebra 
are two distinct articular facets, each receiving part of the head of the first and second 
ribs respectively. The same occurs in the two following vertebree, though the facets are 
less distinctly marked, the head of the rib apparently articulating chiefly to the inter- 
vertebral substance in front of its own vertebra. In the fourth, and more distinctly 
in the fifth and succeeding vertebrie, there is a strongly-marked articular facet on the 
anterior edge of the body, while that on the posterior edge has entirely disappeared (a 
condition, it will be observed, never found in the true Delphinide). Hereafter each 
rib is solely articulated to its own vertebra, and its lower attachment becomes moved 
by degrees from the anterior edge to the middle of the body. As far as the seventh 
vertebra the rib has a double attachment; but in the eighth the upper and lower arti- 
cular surfaces (that on the arch and that on the body) have coalesced, though the part 
that originally belonged to the transverse process and that on the body are distinctly 
recognizable. ‘This coalescence, however, becomes more complete; and, by the diminu- 
tion of its upper part, the articular facet, at first elongated vertically, becomes oval in the 
opposite direction in the eleventh vertebra, and also begins to rise out from the body as 
a short thick process. This process is somewhat elongated and flattened in the twelfth, 
and notably so in the thirteenth vertebra; and at the same time the articular surface be- 
comes gradually reduced in size, corresponding with that of the head of the rib. We have 
thus among the toothed Whales a third method by which the transformation from the 
first thoracic vertebra with its doubly attached rib, to the last with its singly attached 
