366 BUREAU OF AMERICAoSr ETHNOLOGY [bull. 52 



than the highest part. Finally, underneath the facet, the inferior 

 border of the arch in the lower Primates projects downward as a 

 well-marked point, of which in the Monte Ilermoso atlas there is 

 only a trace; in the Indian atlases there is either a siinilar trace or a 

 total absence of this point. 



The tubercle for the transverse ligament is fairly well represented, 

 being, as in a large proportion of modern human atlases, more devel- 

 oped on the right, less so on the left side ; and the same is true of the 

 vertical groove on each side between the odontoid facet and tliis 

 tubercle. The groove here referred to is less differentiated in or 

 absent from the Primates lower than man. 



The pit just back of each transverse ligament tubercle (the ento- 

 glenoid fossa of Macalister) is of submedium development, especially 

 on the right, but similar conditions are often observed in man. In 

 the anthi'opoid and other apes there is no pit at all, or it is small and 

 shallow. 



The oblique ridge ascending from below the fossa just mentioned 

 to the hinder part of the median border of each upper articular facet, 

 which is present as a rule in modern human atlases but is wanting or 

 only feebly represented in lower Primates, is well-defined on both 

 sides in the Monte Hermoso specimen. 



The posterior arch is stout but this feature to the same or even 

 greater degree is quite common in modern man; in most of the 

 anthropoids and monkeys, on the other hand, this arch is more slender 

 than the average in man. 



The posterior arch is also high in its middle third, its maximum 

 expanse measuring 12 mm. This is a less common, though not 

 strictly a very rare, feature among human atlases, being equaled 

 or exceeded by 8 of the 100 atlases used for comparison in the United 

 States National Museum and by 7 out of 30 South American Indian 

 atlases examined at the La Plata Museum. Among the anthro- 

 poid and other apes, however, the posterior arch is usually of only 

 moderate height and where it is relatively more expanded in the 

 vertical direction, as in some of the monkeys and rarely in an excep- 

 tionally powerful anthropoid ape, its height is quite uniform from 

 side to side and is not concentrated, so to say, in the middle portion, 

 as in the Monte Hermoso and other human atlases (pi. 61). 



The proximal parts of the posterior arch in the Monte Hermoso 

 atlas are flattened above and below, tliis feature being characteristic 

 of all human atlases. An approximation to this is occasionally seen 

 in the gorilla, but in all the lower anthropoids and apes the superior 

 and inferior flattening is absent and the oblique sagittal diameter of 

 the arch at these points is smaller than the vertical. 



The curve of the posterior arch is slightly less than the average in 

 human atlases, but equals or approximates that of a fair proportion 



