NO. 3 



COMPARATIVE HISTOLOGY OF FEMUR FOOTE 



7 



thicker in mammals than in birds, and the canal is smaller and the walls are 

 thicker in bats than in other mammals. 



Third. — The medullary index in the human race, as a whole, is 38.6% and, 

 therefore, much lower than in other mammals, in which it averages 63.3% ; that 

 is, the medullary canal is relatively smaller and the wall of the bone thicker 

 in bipeds which carry the weight of the body on two legs than in quadrupeds 

 which carry the weight on four. The three races, however, show slight varia- 

 tions. In all, 139 human femora were examined — 34 black, 23 Indian (pre- 

 Columbian), 9 ancient Egyptian, and 73 modern white. Their respective indices 

 were 41.9%, 43.8% , 39.5%, and 35.8% . From these it will be seen that the index 

 is higher in the ancient than in the modern white femora (counting the Egyptian 

 as of white race), and lower in the modern white (35.8% ) than in the modern 

 black (41.9% ) or the pre-Columbian Indian (43.8% ). That is, the canal is larger 

 and the mass of bone smaller in ancient (Egyptian) than in the modern white 

 femur, and the canal is relatively smaller and the bone larger in the modern 

 white than in the modern black race or the pre-Columbian Indian. The smallest 

 canal and thickest wall were found in the modern white, and the relatively 

 largest canal and thinnest wall in the Indian. Some of these detailed differ- 

 ences may, of course, be purely accidental, due to the insufficient number of 

 specimens, or other conditions ; but they are of sufficient interest to warrant- 

 further observations. 



Medullary Canal 



The canal presents many peculiarities in position, shape, size, surface, and 

 contents. 



In some femora it is situated eccentrically. This is more especially true of 

 human fetal bones, where the canal occupies the anterior half of the cross- 

 section. It is also true in many adult femora of the triangular shape and third 

 (or Haversian) type. In femora of the first type of structure (the lamellar), 

 the canal is situated almost centrally, as such femora do not often have a well- 

 defined linea aspera. In still other cases it is situated obliquely, as in some 

 human femora. 



The shape of the canal seldom corresponds with the peripheral outline of 

 the bone, and the wall of the femur, therefore, is not of uniform thickness 

 excepting in round bones with central canals, and these are generally limited 

 to small femora, to those of the young, and to simple types. In adult bones, 

 the canal varies considerably in shape. In some bones it is nearly circular with 

 fairly regular outlines, as may be seen in the small first type (lamellar) femora 

 like those of the bats. In others it is elliptical or irregular, regardless of the 

 shape of the bone, as in some human specimens. 



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