412 CETACEA. 



Chevron bones. — These structures begin between tbe 34th and the 35th 

 Tertebrse, and the first consists generally of two bones not united in the middle line, 

 but articulating by two surfaces to the anterior and posterior borders of the 34th 

 vertebra, and from the cu'cumstance that it is so connected to the vertebra it would 

 appear to consist of two pau's of bones united. In the next pair the bones of the 

 opposite sides are also separate, but in all the succeeding bones, as far as the 19th, 

 they are united, and each forms an arch across the vessels, but beyond that point 

 they are again resolved into two. They attain their maximum development between 

 the 43rd and the 44th vertebrse. 



Mibs. — The ribs are transferred to the transverse processes at the 8th dorsal, 

 and in this respect Orcella differs from Globicephalws and Orca, in which the 7th rib 

 is not attached to the body of the vertebrse, but is wholly transferred to the transverse 

 process. The one or two pairs of free ribs He iu the muscles of the side at a consider- 

 able distance from the vertebral column. There are nine well ossified sternal ribs, 

 and five of these on each side are apjolied to the side of the sternum. The first 

 rib is articulated to the anterior external angle of the sternum. The ribs conform 

 to the characters distinctive of the DeljpMnidcs. 



Sternum. — This bone has the general features characteristic of the sternum of 

 the Delpliinidce, with an emarginate anterior border, the bone attaining its greatest 

 breadth behind the attachment of the first rib, where it outwardly dilates into 

 two processes, most marked in O. fluminalis. The anterior border is notched in the 

 latter species, but in 0. brevirostris the primordial fissure has closed anteriorly, but 

 enclosing a rounded imperfection of ossification distinctive of many Cetacean sterna. 

 In the hinder end of the bone, the remains of the primordial fissure may either be 

 indicated by a deep notch, as is generally the casein O. fluminalis, or by a groove in 

 0. brevirostris. There are no traces of ossified mesosternal segments. 



The sternum of the gravid female of 0. brevirostris retained its original two- 

 fold nature, being mesially divided into two halves, and only two ribs were 

 attached to it, and that unsymmetrically, the left being considerably anterior to the 

 right rib. 



Tectoral limb : Scapula. — This bone has more antero-posterior extension than 

 in either Globicephalus, Orca, or Fhoccena, and is especially distinguished from the 

 scapulae of these genera by the broad sweep of the supra-scapular border and the 

 downward arching of the coracoid and glenoid borders, which are of nearly equal 

 length, their angles being nearly iu the same plane. The acromion is long, narrow, 

 and slightly downwardly curved. 



Sumerus, radius, and ulna. — These bones do not call for any special description, 

 as their forms vary but httle in the Cetacea, but it may be observed that the 

 humerus is relatively longer than in Orca, having more the proportions that this 

 bone bears to the other bones in Globicephalus. The same is also true of the radius 

 and ulna. 



Manus. — The second finger is the longest, and is relatively longer than the 

 corresponding finger in Orca, and considerably relatively shorter to the rest of the 



