hrdliCka] skeletal REMAINS OF EARLY MAN 365 



the atlases of relatively modern Indians, for in the series of 100 of the 

 latter used for comparison there were found 17 in which the greatest 

 antero-posterior and also the greatest lateral diameter of the opening 

 were either equal to those of the Monte Hermoso atlas or had one 

 diameter equal and the other smaller, and there were two in which both 

 the dimensions were smaller. (See pi. 60.) A female Calchaqui atlas 

 (No. 7-C in the La Plata Museum) approximates also very closely 

 the Monte Hermoso specimen in this respect. 



In shape the central aperture approximates a metal ax and is 

 entirely humanlike, differing considerably from that of any other 

 primate. (See pis. 60, 63. ) The anterior portion is somewhat narrow, 

 owing to marked development of the lateral masses, and the posterior 

 arch is rather shallow, but both of these characters only distinguish the 

 bone still more fully from that of the anthropoid and other apes, in 

 which the anterior part of the central aperture is as a rule broad, 

 wliile the arch of the posterior portion in most cases is deeper than the 

 average in the human species, and especially deeper than that in the 

 Monte Hermoso specimen. On the other hand a considerable number 

 of the Indian atlases compared show precisely the same type of 

 aperture. Absolutely exact duphcation can scarcely be expected, of 

 course, in a feature liable to so much individual variation, but the 

 same is true of the aperture of any other human atlas, or of any of the 

 more important parts of the bone. 



The anterior arch is entirely human in form. The tubercle extends 

 vertically over nearly the whole extent of the arch in the median 

 line, as in modern man; in most of the apes it is confined to the lower 

 part of the arch. From the anterior tubercle to each lateral mass 

 the anterior surface of the arch is flat and more distally it is percepti- 

 bly concave, as in most human atlases; a similar condition was 

 found in a baboon {C. porcarius), but in the anthropoid and most 

 other apes the anterior surface of the lateral parts of the arch near 

 the tubercle is decidedly convex and only seldom is there a sign of 

 the more distal depression. 



The maximum height of the anterior arch, which corresponds to 

 its middle portion, is 11 mm. and its thickness in the median line is 

 6 mm., both dimensions met with in many modern human atlases. 



The facet for the odontoid is large and slightly higher than broad 

 (13 by 11.5 mm.), as in many human atlases with higher anterior 

 arches, but is radically different from what obtams in all other 

 Primates that could be compared, for in these the facet is of greater 

 breadth than height, besides differing more or less in shape from that 

 in man and also from that in the Monte Hermoso specimen. The 

 axis of the facet in the Monte Hermoso atlas is vertical, as it is in 

 most cases in man, while in the apes it is generally more or less 

 inclined in such manner that its lowest portion is more anterior 



