no. 3 comparative histology of femur foote 5 



Density of Bone 



This quality of bone was estimated by its weight and the subjective feeling 

 experienced during the process of grinding, and was found to be far from 

 uniform. Hardly any two bones were the same in this respect. Some were 

 heaxj and others were light; some were hard and others were soft. In some, 

 one portion of the wall was hard and another was soft, and in still others there 

 were soft and hard spots. Tlie femur of tlie hippopotamus was extremely heavy 

 and exhibited a stone-like quality in grinding, while that of the peahen, turkey- 

 buzzard, or eagle was light and had a flint-like character. Many mammalian 

 and human femora were found to vary greatly in the densities of the different 

 portions of their wall. The outer was soft and the inner hard, or vice versa. 

 This was noticed more especially in human femora. Many human bones also 

 had small areas of unequal hardness which were sometimes accounted for by 

 senile changes. Finally, sections of some femora — as those of the elk — seemed 

 to show an extremely brittle character. 



In some cases these inequalities could be explained by histological varia- 

 tions; while in others the chemical character of the inorganic compound seemed 

 to govern the hardness. As a rule, first and second type bones (lamellar and 

 laminar) ground more easily tliau tliird (Haversian system), as might be 

 expected. But the femur of the ])eahen had flinty hardness and yet showed an 

 incomplete second type of structure. This could only be explained by some 

 peculiarity of its inorganic composition. 



Measurements 



The following measurements of each cross-section were taken: the antero- 

 posterior and lateral diameters of the bone and the same diameters of the 

 medullary canal. All measurements were recorded in millimeters. The results 

 will be found in the synoptic tables and also at the beginning of each detailed 

 description. The measurements will give a correct impression of the relative 

 diameters of the shafts of the various femora, and upon them are based the 

 calculated ratios of the medullary canals to their respective bones. 



Medullary Index 



The ratio of the square of the mean diameter of the medullary canal to 

 that of the surrounding bone, as determined from cross-sections of the middle 

 portions of the various femora, is referred to as the medullary index. It has 

 been calculated from the formula below.' The individual indices will be found 



a and 6 are the long and short diameters of the medullary canal 

 respectively. A and B are the long and short diameters of the bone 

 =R. respectively. R is the ratio of the medullary canal to the bone. 



The calculations were made by William P. Rigge, S. X, Professor of 

 Astronomy, Creighton University, Omaha, Nebraska. 



