VERTEBRATA. 



Class MAMMALIA. 



Order CETACEA. 



The order Cetacea exhibits within itself forms of the widest diver- 

 gence. Conforming in general to the fish-like form of body, the 

 members show variations in size between Balaenoptera sibhaldii, 85 to 

 90 feet long, and Platanista about 4 feet; in dentition from the car- 

 nivorous form of Orca to tlie baleen plates of tlie Kight Whale or the 

 almost toothless Monodon. The superficial fish-like characters of the 

 body are generally regarded as degenerative adaptations to the aquatic 

 habitat. The almost total loss of the hair, the equally complete loss 

 of the hind limbs, the flipper-form of the fore limbs and the develop- 

 m.ent of hyperphalanges; the position of the external nostrils on the 

 upper part of the skull; all these are found in general in animals 

 originally terrestrial in habit, that have become aquatic. To these 

 characters should be added the broad, flat tail developed in the hori- 

 zontal instead of the vertical direction and devoid of bony support. 



The following features of the skull have been mentioned by Beddard * 

 as characteristic of the Cetacea: 



" The separation of the two parietals by the intervention of the 

 supra-occipital, or their concealment by its overlapping. 



" The overlapping of the muzzle generally by the premaxillae. 



" The loose attachment between the various bones surrounding or 

 connected with the organ of hearing. 



" The absence or feeble development of the coronary process of the 

 lower jaw." 



The scattered locations and the fragmentary condition of the material 



• a Book of Whales. Putnam & Sons, New York, 1900. This book contains a 

 most valuable semi-popular account of the Cetacea. 



