1897.] Anthropology. 645 
the other light was 6 meters or less; if the nearer light was 10 meters 
distant or more, the wrong answers predominated ; the threshold value 
was about 7-8 meters, or a difference of 17-18 meters. Another 
set of experiments was tried in which the subject was asked to estimate 
binocularly the absolute distance of a single light. The results showed 
no approximation to the truth, the estimates for 50 meters being in 
several cases nearly the same as those for 5 meters. According to the 
author, the muscle sensations—in this case of convergence—play no 
appreciable part here ; it is only the bi-retinal assimilation of correspond- 
ing points that determines our sensation of depth. Thus our percep- 
tion of depth, in so far as it is a sensation at all, and not a judgment, is 
really a visual function, and not a muscular one, as the commonly 
accepted theories incline to believe. The results seem to show that the 
visnal sensation horizon is about 220 meters from the eye. The spheri- 
cal shape of the heavens is due to the practical parallelism of all objects 
further than that distance, as determined by the minuteness of bi-retinal 
localization, rather than to the absence of changes of accommodation 
and convergence for greater distances. —H. C. W. 
ANTHROPOLOGY. 
On Fossil Bird-Bones Obtained by Expeditions of the 
University of Pennsylvania from the Bone Caves of Ten- 
nessee.—On the 20th of last June (1896) the writer received from 
Professor E. D. Cope a small collection of subfossil bones obtained by 
Mr. H. C. Mercer while in charge of explorations for the University of 
Pennsylvania in the Bone Caves of Tennessee. These bones were 
kindly sent to me for the purpose of having them identified if possible, 
and eventually described and figured. As in the case of many cave 
bones, they are not encased in any matrix, being to some degree pliable 
rather than brittle and completely fossilized. They have a rather pale 
clayey color, and not more than one in a dozen of them are perfect. 
Indeed, it is unfortunate that so many of them are in too fragmentary 
condition to be identified with any degree of certainty, and in the case 
of a few mammal bones I found in the collection no attempt was made 
at identification at all. Skulls and sternaare entirely absent from this 
collection, nearly all the specimens being long bones, with the excep- 
tion of the sacral portion of one pelvis; a few coracoids and portions 
1 This department is edited by H. C. Mercer, University of Pennsylvania. 
