INIA GEOFFEENSIS AND PONTOPORIA BLAINVILLII. Ill 



2. Odontoceti or Delphinoidea. Teeth always developed after birth, and generally 

 numerous, sometimes few and early deciduous. No baleen. Olfactory organ rudi- 

 mentary or absent. External respiratory aperture single. Upper surface of the 

 skull generally, if not always, unsymmetrical. Hinder end of the maxilla ex- 

 panded, and covering the greater part of the orbital plate of the frontal bone. 

 Lachrymal bone either inseparable from the jugal or, when distinct, very large 

 and forming part of the roof of the orbit. Kami of mandible nearly straight, 

 much expanded in height posteriorly, and coming into contact in front by a surface 

 of variable length, but always constituting a true symphysis. Sternum almost 

 always composed of several pieces placed one behind the other, and always con- 

 nected with several pairs of ribs, either by cartilage or by distinct costo-stemal 

 bones. Many of the ribs with capitular processes developed, and articulating 

 with the bodies of the vertebrae. 



It is not necessary to pursue further the arrangement of the Mystacoceti, as it has no 

 direct bearing upon the subject of this memoir, and as moreover I have no reason to 

 make any alteration in the divisions into families and genera sketched out in the paper 

 above referred to. 



The subdivision of the Odontoceti, according to their structural affinities, presents at 

 first sight considerable difficulty. To relate all the various attempts, more or less 

 successful, that have been made to unravel this problem would be out of place here. 

 I will only add one more to the number, founded chiefly on an examination of the 

 osteological characters of the principal members of the group*. 



In seeking for some starting-point fi-om which to commence the formation of a 

 natural division of the Toothed Whales, one has occurred to me which I have not found 

 hitherto noticed. The strong and well-defined bones which connect the ribs with the 

 sternum, ossified even at birth, common to the Porpoise, true Dolphins, and their 

 nearest allies, are represented even in the adult Hyperoodon by an entu-ely unossified 

 cartilage. In the four skeletons of Pkyseter macrocephaliis that I have had the oppor- 

 tunity of examining, I have looked in vain for sterno-costal bones, some of which would 

 certainly have been preserved if they approached in relative magnitude and density 

 those of the true Dolphins. In answer to my inquiries on the subject. Dr. George 

 Bennett has kindly informed me that, in both the skeletons of the genus Kogia, now 

 mounted in the Sydney Museum, the cartilages are unossified ; and I am indebted to 

 Professor Van Beneden for similar information respecting the skeleton of the ziphioid 

 Microjiteron preserved in the Zoological Museum at Brussels. From these facts, I think 

 that we may safely infer that the absence of ossified sternal ribs is a character common 

 to the large natural group which includes Physeter, Hyperoodon, and the Ziphioids. To 



* The arrangement here proposed nearly coincides with that arrived at hy Professor Huxley and myself, 

 when discussing this subject together before the delivery of the course of Hunterian Lectures at the Boyal 

 College of Surgeons for the present year (see 'Lancet,' 1S6G, vol. i. p. 381). 



VOL. VI. — PART III. B 



