ACKNOWLEDGMENT 



This work has been largely of a pioneer nature. Tlie zoological classification 

 of animals has furnished tlie principal guide in the selection of bones and in the 

 general plan of study. Beginning with the amphibians and closing with man, one 

 femur after another has been examined until sufficient data have been accumu- 

 lated to establish, to a reasonable degree, definite bone types and type combina- 

 tions which were then employed as a structural basis for comparative study. 



In an investigation of this character, covering a period of more than five 

 years and involving many details, it will not be surprising if imperfections are 

 found; but all possible effort was made to eliminate those that could be detected. 



The study has brought to light a number of important new facts. Among 

 other conclusions the author finds that three types of minute structure form the 

 basis of all bones. The first and second types predominate in amphibians, rep- 

 tiles, and birds, the third in mammals and man. The first type, composed of 

 lamellae, appears as a uniform structure or in a twofold or threefold division, 

 and characterizes the amphibians, lizards, and bats. The second type (laminar) 

 appears first in the amphibians and in an early or late form of differentiation 

 in birds and lower mammals. The third type (Haversian system) is first out- 

 lined in the amphibians and reaches its highest development in the higher mam- 

 mals and especially in man. 



For valuable material, facilities for study and courtesies extended, the 

 writer is especially indebted to the Division of Physical Anthropology of the 

 United States National Museum, to the Divisions of Mammals and Reptiles of 

 the same institution, to the Departments of Reptiles, Birds, and Mammals of 

 the American Museum of Natural History, to the Nebraska State Hospital, and 

 to the Departments of Anatomy of the Northwestern, the Tulane, the Nebraska, 

 and Creighton Universities. 



Furthermore, he desires to express his deep sense of obligation to those 

 who have assisted him: to Dr. Ales Hrdlicka for his encouraging interest and 

 most valuable suggestions in the pursuance of the study, witliout his clearing- 

 house advice the tedious details would have fallen into a useless mass; to 

 Creighton University for apparatus and material assistance in the publication 

 of this report; to Professor William F. Rigge for the calculation of the medul- 

 lary indices; and to the many stutlents and friends who have rendered assist- 

 ance in every possible manner. 



J. S. FOOTE. 



