348 BUREAU OF AMERICAN ETHNOLOGY [bull. 52 



distinct, can not be absolutely excluded, but this would imply the 

 existence at Monte Hermoso of two jJrecursors of man, which appears 

 to me for the present, I shall not say impossible, but highl}" improb- 

 able; and until further proofs appear to the contrary it seems to me 

 more logical and prudent to refer the two specimens to but one form," 



As to the morphologic peculiarities of the atlas, Ameghino ex- 

 presses, to start with, the opinion that the atlas is beyond doubt 

 "not only one of a primate, but it belongs to the same group which 

 includes man and the anthropomorphs." It is further seen that the 

 bone belongs to the ''family of Ilominidse and not to that of the 

 Antropomorpliidse." The features whicli demonstrate that the 

 specimen does not belong to Homo but to a distinct and extinct 

 genus are: The contour of the vertebral canal, determined by the 

 ventral curves of the anterior and ])osterior arches of the atlas, 

 approximates in man an ovoid figure with its longer axis in the antero- 

 posterior direction, while in the Tctraprothorno the figure is elliptical 

 and its greater axis is transverse. "This character is fundamental 

 and separates neatly the Tetraprothomo from the genus Homo. . . . 

 Certain other detailed features in the shape of tlie aperture approxi- 

 mate this bone to that of man." 



The plane for the odontoid facet is vertical, indicating a "per- 

 fectly erect position of the bod3^" The anterior tubercle of the bone 

 presents the same form and development as in man. 



As to the posterior arch, a feature which is }>articularly accentuatetl 

 is the absence from the Tetraprothomo bone of the bridge covering 

 the gi'oove for the vertebral artery. "In the larger part of the mam- 

 mals and in all the living Primates of the Old World, with the excep- 

 tion of the anthropomorphs and man, this vertebral groove presents 

 itself covered by a bony arch; in Tetraprothomo this bridge does not 

 exist, in which it agrees with man and the anthropomor})lis. It is 

 clear that the absence of a bridge over the vertebral arteiy groove is 

 a primitive character and, although there are examples of human 

 atlases in which the gi'oove is totally or partially covered by an arch, 

 these examples do not prove the existence of this bridge in man's 

 precursors but indicate the commencement in man of a tendency 

 toward tlie formation of the bridge. . . . 



"This characteristic is of capital importance in a question of the 

 relations of the distinct families of the Primates. It proves that 

 man and the anthropomor})hs constitute a great group or order 

 {Anthropoidse), which has no immediate relation either with the 

 Lemuridse or with the catarhine or ))latyrhine a})es, and which has 

 remained isolated, evolving independently, probably since the Upper 

 Eocene." 



Other very detailed features regarding the canals and grooves of 

 the vertebral artery are discussed but the text is so involved that it 

 is necessary to refer the reader to the origmal. 



