492 ANTHROPOLOGY: F. BOAS Proc. N. A. S. 
which was elaborated by Mr. I^esUe Spier. Other material was placed 
at my disposal by Dr. Carl Roese of Dresden, whose investigations on the 
relation between anthropological form and the condition of teeth are of 
fundamental importance, and finally I used a large series of casts found 
in the offices of orthodontists, for which series I am obliged to the good 
offices of Dr. Hellman. The series previously published by me suggested 
that the difference in period which characterizes the development of the 
two sexes, is not found in the development of the teeth. As I have pointed 
out before, the development of the head shows, that a sexual difference 
amounting to about IV2 years in the rate of physiological development 
occurs about the fifth year, and we know that this difference increases 
to a little more than two years at the time of maturity. The time of the 
eruption of the permanent canines and of the premolars is between the 
tenth and eleventh years. During this time the normal difference in 
regard to physiological development between the two sexes is approxi- 
mately a year and one-half, perhaps a little more. For the teeth, how- 
ever, we obtain a difference of less than V2 a year, which shows clearly 
that the dentition of males and of females must possess definite secondary 
sexual characteristics. An investigation of the size of the teeth does not 
bring out any very striking differences. B. Mlihlreiter { Anatomic des 
menschlichen Gehisses, Leipzig 1891, pp. 128, 129) in his investigations of the 
teeth, has suggested that there are characteristic differences in form. 
Further investigations, however, will be necessary in order to show whether 
the physiological difference in development is accompanied by a mor- 
phological difference in form. 
I expected that, if there should be physical retardation, we should find 
among the children of the well-to-do an early development of the per- 
manent teeth and among the children of the poor, a later development. 
However, just the reverse was found. The eruption of permanent teeth 
among institutionalized children showed an acceleration of approximately 
eight months. I think this puzzling phenomenon may be explained by the 
fact that in the dental care of institutional children there is a strong 
tendency to remove the deciduous teeth as soon as they show decay, and 
that the removal of the teeth acts as a stimulus upon the development of 
the permanent teeth. Possibly the conditions in Porto Rico, where we 
also find an unusually early eruption of permanent teeth combined with a 
marked retardation in the development of stature, may be explained in a 
similar way ; namely, by early decay of deciduous teeth which brings about 
an early loss of the teeth. I am still engaged in an investigation of the 
eruption of the deciduous teeth in relation to bulk of body and I hope to 
report on this subject at a later time. 
The evidence that may be derived from a study of stature and weight 
alone indicates that the under-development of the children in charitable 
institutions is due to retardation. 
