NO. 3 



COMPAKATIVE HISTOLOGY OF FEMUR FOOTE 



17 



FeEQXJENCY OF OCCURKENCE 



The distribution of the three types of bone, tlieir stages of development, 

 and divisions may be seen in the following table: 



DISTRIBUTION OP THE THREE BONE TYPES AND THEIR DIFFERENTIATIONS 



Type 



Number of femora examined.. . 



Lamella', uniform throughout. . 



Lamella', twofold division 



Lamellfe, threefold division.... 



Lamellae as cancellous bone. .. . 



Lamellie as important bone 



structure 



Amphib- 

 ians 



II. 



LaminiB, incomplete differen- 

 tiation 



Lamina;, complete differentia- 

 tion 



Laminie as important bone 

 structures 



III. 



Haversian system, la 



Haversian system, lb 



Haversian system, Ic 



Haversian system, C 



Haversian system, incomplete 



differentiation 



Haversian system, complete 



dilferentiation 



39 



Per cent 



2C 



ijl 



20 



3 



i 100 



i 



5 







5 



21 

 n 



CI 

 



21 







Reptiles 



34 



Per cent 



60 



17 



6 



17 



100 



9 







9 



21 



23 











52 







Birds 



40 



er cej 



30 



7.5 



5 



5 



47 



25 







25 



5 



7 



82 







Fetal 

 man 



Total 



440 



Per cent Per cent 















100 



100 



100 







100 



14 



71 











18 







19 



14 



4 



46 



79 



18 



1.4 



21 



27 



15 



7 



54 



46 



54 



Looking over the above table it will be noticed that lamellae, in some stage 

 of differentiation, form an important part of the majority of all femora, and, 

 therefore, may be considered as the simplest, oldest, and most universal bone 

 units; that the first type of Bone, without concentric divisions, has a wider 

 range than it has ivith concentric divisions, and that cancellous bone — which is 

 first type with a special arrangement of lamellae— is found in all classes of 

 animals; that laminae — incomplete or complete — are found in the smallest num- 

 ber of femora, and that Haversian systems, in some stages of differentiation, 

 are found in the largest number of femora and to the greatest extent in man. 

 The early differentiations of the Haversian systems are found in 46% and the 

 late in 54% of all femora examined. There are more early differentiations in 

 the lower animals and more late differentiations in man than in the lower 

 animals. Early and late differentiations may occur in the same bone and more 

 especially in mammals and man, as may be seen in such femora as represented 

 in plate 31, figure 399. 



two lamiMce occurred at intervals. Around these enlargements two to four concentric lamellae were 

 arranged, the whole figure presenting the appearance of a small Haversian system (pi. A, fig. P). 

 These are referred to in the detailed description as aberrant forms of the Haversian system. 



