MAMMALIA. CETACEA. 357 



The group includes among others the Right whale (Balaena), 

 Humpbacked whale (Megaptera), and Rorqual (Balaenoptera). 



Suborder (3). ODONTOCETI. 



Teeth always exist after birth and baleen is never present. 

 The teeth are generally numerous, but are sometimes few and 

 deciduous ; the dentition is homodont (except in Squalodori). 

 The dorsal surface of the skull is somewhat asymmetrical, 

 there is no trace of an olfactory fossa, the nasals are quite 

 rudimentary, and the hind ends of the maxillae cover part of 

 the frontals ; in all these respects the skull differs from that 

 of the Mystacoceti. The lachrymal may either be united to 

 the jugal or may be large and distinct. The tympanic is 

 not ankylosed to the periotic. The rami of the mandible are 

 nearly straight and become united in a long symphysis. Some 

 of the ribs have well developed capitula articulating with the 

 vertebral centra. The sternum is almost always composed of 

 several pieces as in other mammals, and several pairs of ribs 

 are connected with it. There are always five digits to the 

 manus, though the first and fifth are usually very little 

 developed. 



The suborder includes the Sperm Whale (Physeter), Nar- 

 whal (Monodon), Dolphin (Delphinus), Porpoise (Phocoena), 

 and many other living forms as well as the extinct Squalodon 

 which differs from the other members of the suborder in its 

 heterodont dentition. 



Order 4. UNGULATA. 



This order includes a great and somewhat heterogeneous 

 group of animals, a large proportion of which are extinct. 

 They all (except certain extinct forms) agree in having the 

 ends of the digits either encased in hoofs or provided with 

 broad flat nails. The teeth are markedly heterodont and 

 diphyodont, and the molars have broad crowns with tubercu- 

 lated or ridged surfaces. Clavicles are never present in the 



