INIA GEOFFEBXSIS AND PONTOPOEIA 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- 

 brae coexisting with it, as in the cei-vical region : or, to explain the case in other words, 

 the anterior ribs in both have an upper and a lower connexion with the vertebras ; 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 Inia 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 vertebrae 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 vertebrae, 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 vertebrae, there is a strongly-marked articular facet on the 

 anterior edge of the body, while that on the posterior edge has entu-ely disappeared (a 

 condition, it will be observed, never found in the true Belphmidte). 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 



