238 A BOOK OF- WHALES 



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the form of the lacrymal bone, which is not distinct 

 from the malar, and consists of a thicker piece, which 

 ends abruptly in a thin bar of bone articulating be- 

 hind with the squamosal. This single bone may 

 contain the elements of the two distinct ossifications 

 of other Cetacea. The skull is asymmetrical, as in 

 other Odontocetes, but there is no such highly-raised 

 crest behind the nares as in the Ziphioids or Sperm 

 whales. The symphysis of the mandibles is of 

 limited extent, " never exceeding one-third of the 



ramus.' 



The most salient difference perhaps which the 

 Delphinidae display from most other whales is the 

 presence of numerous functional teeth in both jaws. 

 It is only the primitive Platanistidae that show agree- 

 ment with them in this. But there are exceptions. 

 In Beluga the teeth show a commencing reduction, 

 and this culminates in the Narwhal, where the well- 

 known tusk only (sometimes double) is left. 



The vertebral column is often composed of very 

 numerous vertebrae, as many as ninety or so having 

 been recorded. On the other hand, it is by no means 

 infrequently short, so that no family definition can be 

 arrived at from a statement of these numbers. But 

 all Dolphins agree in the mode of articulation of 

 the ribs. At first they are double-headed, afterwards 

 the tuberculum only is left ; furthermore the sternal 

 ribs are ossified. 



The Delphinidae enumerated in Dr. Gray's Cata- 

 logues amount to over one hundred in number ; and 

 even so careful a worker as Mr. True enumerates 



