500 CETACEA. 



Platanist in which the ribs are attached direct to the bodies of the vertebrae in 

 the sixth, seventh, eighth and ninth vertebrae, owing to the entire absence of any 

 uitervening process or projection from the bodies of these vertebrae, and owing 

 perhaps to the imperfectly developed character of the transverse processes, the latter 

 appear suddenly to cease, whereas in the adult the transverse processes appear gra- 

 dually to subside on to the bodies of the vertebrae and to exist as tolerably well 

 marked short processes even on the eighth and ninth vertebrae on which in the 

 young there is no trace whatever of such a process, the structures afterwards deve- 

 loped in these as in the seventh also being only outgrowths of the bodies of the 

 vertebrae. The process bearing the tenth rib is entirely different, and is a distinct 

 structure developed quite independently from a centre of its own. These processes 

 are apparently developed from behind forwards, as in a young skeleton those of the 

 caudal and posterior portion of the lumbar region are firmly united to their vertebrae, 

 while those bearing ribs and a few behind them are not so united to their segments. 

 Platanista in having eight lumbar vertebrae more resembles Po7itoporia than 

 Inia, as the former, according to Burmeister, has six or seven' lumbar vertebrae, 

 whereas Inia is stated by Elower to have only three or four, which is a marked 



difference from what prevails in the ordinary Delphinidce, in which the lumbar region 

 has great extension. 



Professor Flower remarks that " nothing can be more dissimilar than the lumbo- 

 caudal region of the special column in Inia and Flatanista," and from Burmeister's 

 researches on the anatomy of Pontoporia we may add, between this dolphin and 

 the G-angetic form. 



In Platanista, as I point out hereafter, the sternal ribs, although cartilaginous 

 in youth, become ossified with adult Life, but always with a small portion of carti- 

 lage or ' intermediate rib,' as in the Monotremes, intervening between the end of the 

 rib and the ossified sternal rib, whereas in Inia the sternal ribs are always cartilao-in- 

 ous. Flower in grouping Platanista, Inia and Pontoporia with Physeter, Hyperoodon 

 and the Ziphioids did so under the impression that the absence of ossified sternal ribs 

 was a character common to them as a group. But now, in addition to the sternal 

 ribs of Platanista being known to be ossified in adult life, Burmeister^ has shown 

 that the sternal ribs of Pontoporia are ossified, as in marine dolphins o-eneraUy to 

 which it is aUied. 



Such facts have an important bearing, as Professor Flower v/ho is facile princeps 

 in this department of anatomy, when seeking for some starting-point or basis for a 

 primary division of the toothed whales, Odontoceti, selected this presence or absence of 

 ossified sternal ribs as " a character derived from a part of the organization apparently 

 less liable to adaptive modifications than the teeth or fins." It would now appear, 

 liowever, that this character has not that reliability which it was thought mio-ht be 

 attached to it. The facts already adduced, and those yet to follow in this contribu- 

 tion to the anatomy of Platanista, seem to me to confirm the just appreciation which 



' Proo. Zo.il. Soc, 1867, p. 485. 

 - Loc. cit., p. 412, 



