YERTEBRATA 



133 



ill most of the lines of the Artiodactyla, which reaches its 

 extreme in the Cameloidea, and in the Booidea. In the 

 most specialized types of these superfamilies but two digits 

 remain, and the metacarpals of these are fused into a single 

 bone, the " cannon bone." This structure first appears in 

 time in the latest Neocene. (Fig. 66.) 



Fig 6ii.— Anterior feet of Artiodactyla, with both series of carpals, except in 

 No. 4. Frnm Kowalevsky. No. 1, Hippopotamus ; 2, Hyopotamus ; 3, Dorcathe- 

 rhim : 4, Gelocus ; 5, Cervus. 



Tiie families embraced in the orders of Eutherian Mam- 

 malia aie the following : 



Marsupialia; (Polyproiodontia) ; Triconodontidse, Amphi- 

 theriidffi, Myrmecobiidse, Dasyuridss, Didelphidse, Per- 

 amelidffi; (Diprotodoidia) ; Phascolomyidse, Phalangist- 

 idse, Tarsipedida3, Diprotodontidje, Macropidse, Thyla- 

 coleonidge. 



Cetacea; (Archieoceii); Zeuglodontidse ; {Oduidoceti) ; Squ&l- 

 odoiitidee, Platanistidse, Physeteridse, Deli>liiind£e,(il/^s- 

 tacoceti) ; Baltenida:. 



Sirexia; Prorastomidse, Halitheriidie, Manatidte, Halicori- 

 da;, Rhvtinidffi. 



