JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. 9 MAY 19, 1919 No. 10 



PALEONTOLOGY. — Significance of divergence of the first digit 



in the primitive mammalian foot. Jamus WilIvIAMS Gidley, 



U. S. National Museum. 



In connection with some recent research work on Basal Eocene 

 mammals I have had occasion to make a critical study of the 

 primitive mammalian foot, especially as regards the meaning 

 of divergence of the first digit. On the interpretation of this 

 character depends in no small degree our concept of the early 

 life history of the Mammalia. 



Based on certain modifications observed especially in the 



hind feet of marsupials, including divergence and opposability 



of the hallux associated with a tendency to enlargement of the 



fourth digit and reduction and syndactylism of the second 



and third digits, Huxley in 1880' expressed the view that 



the existing marsupials have been derived from an 



arboreal ancestry. Later Dollo,- in full accord with this 



view, discussed the evidence for it at considerable length. vSoon 



followed a review by Bensley^ in which he expressed general 



agreement with the interpretation of Huxley and Dollo. 



In 1904 Matthew published an article on "The Arboreal 



Ancestry of the Alammalia,"' in which he accepted the 



views of Huxley, Dollo, and Bensley regarding the arboreal 



ancestry of the marsupials, and expressed his belief that the 



^ Proc. Zool. Soc. Lond., p. 655. 



' Les ancetreses Marsupiaux etaient-ils arhoricoles? Miscellanees biologiques, 

 1899. 



^ Amer. Nat. 35: 117-122. 1901. 

 ^Amer. Nat. 38:813-815. 1904. 



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