SKELETON OF THE WHALE. 153 



tribe. But the following osteological characters are both 

 common and peculiar to the mammalia. The squamosal, 

 27, or second bone of the bar continued backwards from 

 the maxillary arch, is not only expanded as in the che- 

 lonia, but develops the articular surface for the mandible, 

 and this surface is either concave at some part or is flat. 

 Each half or ramus of the mandible is ossified from a 

 single centre, and consists of one piece ; and the condyle 

 is either convex or is flat, never concave. The presphe- 

 noid (centrum of the parietal vertebra) is developed dis- 

 tinctly from the basisphenoid ; it may become confluent, 

 but is not connate, therewith. 



One known mammal (the three-toed sloth) has more, 

 and one (the manatee, or sea-cow) has less than seven 

 vertebrse of the neck. In the rest of the class these 

 vertebrae, which have the pleurapophyses short and 

 usually anchylosed, are seven in number. 



SKELETON IN THE CETACEA, OR WHALE TRIBE. 



In the skeleton of the whale (Fig. 25), Avhich to out- 

 ward appearance seems to have as little neck as a fish, 

 th^re are as many cervical vertebrre as in the long-necked 

 giraffe: this is a very striking instance of adherence to 

 type within the limits of a class : the adaptation to form 

 and function is effected by a change of proportion in the 

 bones ; the cervical vertebraa in the whale are flattened 

 from before backwards into broad thin plates; in the 

 giraffe (Fig. 80) they are produced into long sub- 

 cylindrical bones. In the whales, the movements of these 

 vertebrae upon one another are abrogated ; and in the 

 grampus and porpoise, the seven vertebra) are blended 



