THE SKULL 



telescoping, or the sliding of some bones over or under others so as to 

 result in bony laminations and shortening of some of the cranial ele- 

 ments, has clearly been from before in a backward direction against the 

 cranium. The maxillaries and premaxillaries have spread backward and 

 to the side so as to override the frontals, the parietals have been crowded 

 far to the side and the interparietal eliminated. In some forms {Kogia) 

 this is so marked that the maxillaries or premaxillaries may actually meet 

 the supraoccipital. There is no tendency for the elimination of the 

 lachrymal as in the pinnipeds, but like the Sirenia this bone becomes 

 thickened and more massive. In practically all living forms the meseth- 

 moids and ectethmoids fuse into a flat bony plate to form the posterior 

 wall of the nares and the nasals are reduced to thickened ossicles above 

 these. The rounded occipital plane has a marked forward inclination, but 

 this is most moderate when compared to conditions in the Mysticeti. 

 Other peculiarities often exist, as the fact that in Platanista the palatines 

 meet the maxillaries and the latter have a remarkable development in 

 broad extensions stretching upward, while in adult males of Hyperoodon 

 there is a comparable development of the premaxillaries. It is not un- 

 likely that these bony extensions are either cause or efl?ect of unusual 

 specialization of the blowhole musculature attached to them. In life the 

 bony passages are approximately vertical, although the angle, from below 

 upward, which they describe with the long axis of the skull is slightly 

 more than a right angle. Thus the nares have migrated as far to the 

 rear as the braincase will allow, and farther, I may add, than would be 

 possible without the recession of the olfactory lobes of the brain. One 

 bony narial aperture is usually slightly larger than the other and this 

 varies individually. In all odontocetes without exception, however, the 

 right half of the facial region of the skull is larger than the left. In 

 other words, the measurement from between the nares to the lateral 

 border of the frontal is always larger upon the right side than the left. 

 And the Odontoceti are the only mammals either living or extinct in 

 which this cranial asymmetry is the normal condition. In some forms 

 it is much less marked than in others, while in the Physeteridae, because 

 of accompanying asymmetry of the bony nares, it is carried to an extreme. 

 All manner of theories, most of them somewhat fanciful, have been ad- 

 vanced to account for it. Abel claimed, without any convincing argu- 

 ment, that it was due to the atrophy of the nasal bones and shortening 

 of the braincase. Kiikenthal believed that a sculling motion of the tail 

 tended to turn the animal to the left, resulting in a thickening of the 

 cranial bones upon that side and a consequent broadening of the right 



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