NO. 8 INTERRELATIONSHIPS OF THE CETACEA WINGE 75 



were true that the caudal fin in cetaceans was usually obliquely set 

 this would j5robably not hinder whales from swimming forward in a 

 straight line if they so wished. That the obliquity of the tail, if it 

 occurs as represented by Kiikenthal, does not in any event necessarily 

 carry with it the asymmetry of the skull is proved by the whalebone 

 whales, whose tail is said to be oblique, but whose skull is without 

 asymmetry in spite of Kiikenthal's word to the contrary. And that 

 the asymmetry of the face is not dependent on obliquity of the tail is 

 proved by Delphinapterus, whose tail, also according to Kiikenthal's 

 interpretation, is not oblique, but whose skull is distinguished by a 

 high degree of asymmetry. Should the water's pressure work most 

 powerfully on the left side of the head it would be difficult, in spite 

 of Kiikenthal's attempt at an explanation, to understand why the 

 bones on the left side of the skull are narrow while those on the right 

 side are broad, or why the nasal passage is pushed over toward the 

 left side, a point that Kiikenthal does not try to argue. Of Kiiken- 

 thal's explanations scarcely anything is left except the knowledge that 

 it is the pressure of the water which is responsible for the asymmetry 

 of the skull in the Odontoceti. Why the water presses obliquely is 

 still unknown, but the reason is not likely to be anything else than a 

 habit in the carriage of the head : the head presumably must be held 

 a little obliquely even when the animal is swimming straight forward ; 

 and the pressure must be strongest on the right side. 



" (P. 24.) On the Squalodontidce see especially : 

 Grateloup : Description d'un fragment de machoire f ossile, d'un 

 genre nouveau de reptile (Saurien), de taille gigantesque, voisin 

 d'Iguanodon, trouve dans le gres marin, a Leognan, pres Bor- 

 deaux, 1840, pp. 1-8, pi. Separate from Actes de I'Acad. des 

 sciences, belles lettres et arts de Bordeaux, vol. 2. Squalodon. 

 H. V. Meyer: Arionius servatus, ein Aleersaugethier der Molasse; 



Palasontographica, vol. 6, 1856, pp. 31-43, pi. 6. Squalodon. 

 Jourdan : Descr. de restes f ossiles de deux grands Mammiferes con- 

 stituant le genre Rhizoprion et le genre Dinocyon ; Annales des 

 Sciences Naturelles, ser. 4, Zoologie, vol. 16, 1861, pp. 369-372, 

 pi. 10. Rhizo prion = Squalodon. 

 Van Beneden : Recherches sur les Squalodons ; Mem. Acad. Roy. 

 Belgique, vol. 35, 1865, pp. 1-85, pis. 1-4, with figures of the 

 upper jaw of 6". antuerpiensis (and of the skull of vS'. ehrlichii = 

 Patriocetus) . 

 Van Beneden : Recherches sur les Squalodons, Supplement ; Mem. 

 Acad. Roy. Belgique, vol. 37, 1868, pp. 1-13, pi., with figure of 

 the under jaw of 5". antuerpiensis. 



