NO. 3 COMPARATIVE HISTOLOGY OF FEMUR KOOTE 3 



to age, size and strengtli of the bone, and possibly to other conditions. It is 

 certainly safe to say that few long Iiones, and particularly femora, have pre- 

 cisely the same structure, and yet, through all their diversity, tliere can be 

 perceived certain definite, readily recognizable strains, which are found not 

 only peculiar to separate groups of animals, but also to definite stages of 

 ditTerentiation. 



The summary which follows will be treated under the following headings: 



General shape. 



Relation of structure to shape. 



Density of bone. 



Measurements. 



Medullary index. 



Medullary canal. 



Medullary contents. 



Medullary surface. 



Cancellous bone and trabeculae. 



Variety of minute structure of tlie wall of the femur. 



Units of bone structure. 



Bone cells — lacunae. 



Dendrites and canaliculi. 



Ditferentiated bone units — Lamellae. 



Uniformly lamellated bone. 



Twofold division. 



Threefold division, 

 riaminae. 



Haversian system. 

 Types of bone structure. 

 Frequency of the occurrence of types. 

 Type combinations. 



Type of bone structure according to classes of animals. 

 The factors influencing tyi)es of bone structure as could be determined from 

 the grade of the animal. 

 Geographic position. 



Sex, age, function, individuality, liealth and disease, heredity. 

 Senility. 



General Shape of the Femora of the Lower Animals 



By the shape of the femur is understood the shape of the cross-section of 

 the bone at its middle. That this sliape of the shaft of the femur varied con- 



