CETACEA. 



709 



The two Sub-Orders of living Cetaceans may be contrasted 

 as follows (after Flower) : 



MYSTACOCETI or BAL^ENOIDEA, 

 baleen Cetaceans. 



ODONTOCETI or DELPHINOIDEA. 

 toothed Cetaceans. 



The teeth are absorbed before birth. 



Whalebone or baleen plates develop as 

 processes from the palate. 



The skull is symmetrical. 



The nasals roof the anterior nasal pas- 

 sages, which are directed upwards and 

 forwards. 



The maxilla does not overlap the orbital 

 process of the frontal. 



The lachrymal is small, and distinct from 

 the jugal. 



The tympanic is ankylosed to the periotic. 



The rami of the mandible are arched out- 

 wards, and have no true symphysis. 



All the ribs articulate only with the trans- 

 verse processes of the vertebrae. 



The sternum is a single piece, and articu- 

 lates with a single pair of ribs. 



The external nostrils are separate. 



The olfactory organ is distinctly de- 

 veloped. 



There is a short caecum. 



Examples : 



The right-whale (Bala>na), the 

 hump-back (Megafitera), the 

 rorqual (Balcenoptera). 



The teeth persist after birth, and are 

 generally numerous and functional. 



There is no baleen. 



The skull on its upper surface is more or 

 less asymmetrical. 



The nasals, often small, do not roof the 

 anterior nasal passages, which are di- 

 rected upwards and backwards. 



The maxilla covers most of the orbital 

 process of the frontal. 



The lachrymal is fused to the jugal, or is 

 large, and helps to roof the orbit. 



The tympanic is not ankylosed to the 

 periotic. 



The rami of the mandible are straight, 

 and form a symphysis. 



Several anterior ribs articulate by capi- 

 tula with the centra of vertebrae. 



The sternum has usually several segments 

 with which several sternal ribs articu- 

 late. 



The nostrils unite in a single blow-hole on 

 the top of the head. 



The olfactory organ is rudimentary or 

 absent. 



There is no caecum, except in Platanista. 



Examples : 



The Sperm whale (Physeter), the 

 dolphin (Delphinus), the por- 

 poise (Phoc&na), the "Gram- 

 pus " (Oreo), the Ca'ing whale 

 (Globicephalus), Grampus, the 

 Narwhal {Monodon), with a 

 horn-like tusk in the male only, 

 the Beluga {Delphinapterus), 

 the blind Platanista of the 

 Ganges. 



