548 CETACEA. 



arches are ossified to tlie tentli caudal, and they becomg more and more faint as they 

 are traced backwards. In the first five they consist of little more than flattened 

 laminge 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 back as the sixth, their sutures being quite intact ; but in the seventh 

 and succeeding vertebrae the transverse processes are exogenous products of the 

 centrum, occupying the position of the autogenous transverse processes, but chiefly 

 developed from the anterior portion of the lateral surface of the centra. The neuro- 

 central 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, but 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 bones, 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 bone 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 bone is placed between the twenty-sixth 

 and twenty-seventh vertebrse, there being in all fifty-one vertebrae in the skeleton. 



Ossification of sternum. — In the youngest specimen, the presternum 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 be viewed, it would appear that the two 

 halves of the presternum 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 presternum. The anterior angle for the articulation of the first rib is cartila- 

 ginous. In the second specimen, the two halves all but meet in the middle line, 

 but 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, but 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- 

 sternal elements become almost, if not entirely, united in 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. 



