8l4 THE AMERICAN NATURALIST. [Vol. XXXVIII. 



Notharctus). Second, in those groups whigh- have not an 

 opposable thumb, we find as we trace back their ancestry that 

 the trapezium, whose form and facets give the surest indication 

 on this point, approaches more and more nearly to the type 

 preserved in the Primates, etc. It becomes large, triangular, 

 with very concave distal facet for the digit, and round-conical 

 proximal faceted end abutting against the scaphoid, trapezoid 

 and centrale. In the four Basal Eocene mammals (Pantolambda, 

 ^aipiotogonia, Cla^nodon and Dissacus) in which this part of the 

 and w'hc ^^^*^/orm of the bone is surprisingly uniform, 



'''' "^'"^"^ P'-it together, the first digit is thrown 

 the rest of the hand, and permits of much 

 (K-,'vc"!',r,!'! ^^'^ remaining digits, with a considerable 



tiMax 1*1,-111 ^^^^^ development of the foot for 



tlicirin',l,ii *'''''^^**^^**" ^^^^ trapezium and first metacarpal lose 

 sel',',-"^'*/' '^'^' ^^^^ rounded conical proximal facet of the former 

 t'-'uKvoid ^'^^ ^""'^^^"^ "^^^ ^"^^^^ scaphoid and 



dist il aid '^Y ^'''''^ ^^c«mes more plane and its whole 

 proxinnlVi ''^^'^^^ ^'""^^^^ appressed against the 



the f urthcT ' 1^^'^ "''^^''"'^ metacarpal, which it overlaps. In 

 reduced "^'^^^ the running foot the first digit is 



usually follov "' ■^'''"''^ finally disappears, and the trapezium 

 (Iviis'soclact'Y trapezoid either remaining separate 



^^^^^^^ ' ''^ ^^^'"^^ consolidated with the magnum (Artio- 



c:Ue(L\!it'X'cl/>r^^'"'^^ ^''"''"^ 



'^■ai ly mamnl^^^^^^^ ^'^'sals. especially the intei-nal cuneifornC in all 

 111' "Y^"^'^ ^'arpus outlined above. ver3-'^strongly suo-<.ests that 



ll-l'-cakHl mo?l'^'^'-''^ terrestrial locomotion began earlier 

 J'l the third nl i(v"if- 'V 

 d'-ne tint the s ■ ''^W^-^^' ^s many anatomists have 

 lanx. anil tint 7hT''''' ^''^ metacarpal is really a proximal pha- 

 Hvpothe>,s th-ul!ll ^'^e ^^u^^ first metacarpal, the 



>,',ji,.v , , ' ' 11 I 1 vsed through a sta-e when the 

 "•'"^x and hallux w.-.- ■'^'tr^'- 



