THE TELESCOPING OF THE CETACEAN SKULL 



Bv GERRIT S. MILLER, JR. 



(With 8 Plates) 



CONTENTS 



PAGE 



Significance of the Word " Telescoping " i 



General Conditions in Zeuglodonts 3 



General Conditions in Modern Cetacea ; Suggestions as to the Possible 



Mechanical Origin of These Conditions 4 



The Three Cetacean Phyla or Series 12 



Key to the Suborders of Cetacea 13 



The Details of Telescoping and Their Relation to Classification 14 



Details in the Baleen Whales 15 



Key to the Families and Genera of Baleen Whales 20 



Details in the Toothed Cetacea 22 



Key to the Families and Subfamilies of Toothed Cetacea 33 



Behavior of the Modern Cetacean Skull 35 



Remarks on the Classification Here Adopted 40 



SIGNIFICANCE OF THE WORD "TELESCOPING" 

 The skeleton of the cetaceans shows more conspicuously than that 

 of any other group of mammals the simultaneous action of two oppo- 

 site trends of modification : the first toward reduction and elimination 

 of those parts which have been rendered useless by a change from 

 an original mode of life to another of a very dififerent kind, the 

 second toward the extreme remodeling of the parts which remain 

 actively functional under such new conditions. The changes of the 

 second type are those which present the greatest interest. Among 

 them the most important are shown by the skull. 



In mammals whose skulls have departed widely from the gen- 

 eralized original form the modifications have usually been made 

 through great changes in the shape or size of individual bones with 

 comparatively little alteration in the mutual contact-relationships of 

 the parts concerned in the process. In the rare instances when such 

 changes of contact-relationship occur, as the extension of the pre- 

 maxillary backward over the frontal above the orbit in the elephants, 

 or the covering of the parietals by the forward advancing occipital 

 shield in the burrowing rodents of the genus Spalax, the changes 

 are recognizable as exceptions to the general course of modification 

 which the skull is undergoing. By the more usual process have 



Smithsonian Miscellaneous Collections, Vol. 76 No. 5 



