1010.] Relations of the Metatheria to the Prototheria and Eutheria. 225 



Acccssonj condijlar foramen. An accessory or second condylar foramen, 

 in front of the main one, seems to be characteristic of both Polyprotodonts 

 and Diprotodonts. Its supposed presence in Creodonts is mentioned below 

 (p. 302). 



VII. Taxonomic History of the Divisions Prototheria, Metatheria 



AND Eutheria.^ 



1816. De Blainville groups the Monotremes and Marsupials as "Di- 

 delphes" in contrast with the "Monodelphes" or Placentals (p. 77). 



1834. De Blainville takes the step he had suggested in 1816 and raises 

 the "Ornithodelphia" (Monotremes) to a rank coordinate with that of 

 "Didelphia" and "Monodelphia." (p. 82). 



1837. Bonaparte uses these two main divisions (see p. 84) under the 

 terms "Ovovivipara" (Marsupials and Monotremes) and "Placentalia." 



1866. Hpeckel, recognizing that the Marsupials and Placentals have 

 been derived from a common stem (later called "Prodidelphia") in his 

 phylogenetic diagrams correctly represents the relations of the three groups. 



1872. Gill uses the term "Eutheria" to include both the Marsupials 

 and Placentals (pp. 92, 230). 



1880. Huxley restricts the term "Eutheria" to the ancestors of the 

 Placentals and invents the term Metatheria for the remote ancestors of Mar- 

 supials plus Placentals. The terms "Prototheria," "Metatheria" and 

 "Eutheria" were used by Huxley chiefly as denoting successive stages of 

 development. 



VIII. Summary of the Genetic Relations of the Marsupials. 



It is generally believed that the earliest mammals had a shoulder girdle 

 of the Monotreme type and were probably oviparous, and reasons have been 

 adduced above (p. 161) for inferring that they were also semifossorial in 

 habits. From this early Prototherian type the Monotremes have departed 

 very widely in many of their skull-characters (p. 150). The primitive 

 Marsupial skull on the whole approaches the Cynodont skull much more 

 nearly than does that of the Monotremes, especially in the general conforma- 

 tion of the lateral aspect, in certain characters of the malar and squamosal 

 (p. 207), in the proximal spreading of the nasals (p. 120), in the long sagittal 

 crest, narrow brain case and relations of the pterygoids (p. 120). But in 



1 The references to this historical summary appear under Part I (see list of references). 



