NO. 3 COMPAKATIVE HISTOLOGY OF FEMUK FOOTE 



33 



The medullary indices diminished from the extremities toward the middle 

 of the shaft, and were lowest 15 to 17 cm. below the section of the head. The 

 band of lamella began 20 to 22 em. below the head, and was most pronounced 

 in the anterior wall. It extended downward toward the lower extremity, and, 

 gradually diminishing in thickness, finally merged into the thin envelope of 

 lamella; surrounding the condyles. Cancellous bone diminished from the ex- 

 tremities toward the middle of the shaft, and was entirely absent from the 

 middle third of the bone. Senile changes, not very marked, were most fre- 

 quent in the middle portion and the anterior wall. 



A section through the middle of this femur, compared witli the remaining 

 sections, did not give as fair a representation of the whole bone structure as 

 the corresponding section of femur No. 300 gave to that bone. However, it 

 did show plainly the type of bone to which this femur belonged. Notwith- 

 standing, the lamellar band in the anterior wall of the lower portion, the 

 characteristic unit of the whole bone was the Haversian system. 



The heads and condyles of both femora were composed almost entirely of 

 lamellae. 



V. SENILITY 



After reaching its highest degree of development, as indicated by the 

 character of its lacuna; and caualiculi, the Haversian system may remain in this 

 condition for a time, but sooner or later the dissociation of the organic and 

 inorganic constituents begins to appear, and the system gradually becomes 

 granular, opaque, and black. The sum total of the processes by which these 

 results are obtained is age or senility. 



An examination of the various sections shows that this condition is more 

 common than would be expected, and that, too, regardless of age in years. 

 A human femur may be more or less senile at 35 or any subsequent age. 



Adult human femora in general show a much larger percentage of senility 

 than the femora of the lower animals. From a review of the various sections it 

 may be seen that senility does not seem to appear at all in the amphibians, 

 reptiles, birds, or bats, and was seen in only five or six of all the remaining 

 mammalian femora; while it is found in the majority of femora of the white 

 human race. Just when the amphibian, reptUe, bird, or mammal becomes adult, 

 just how long this period of life lasts, or when old age sets in, are not known. 



The fact that senile changes are so prominent in the lamella; of Haversian 

 systems and so infrequent in the lamellfe of other situations suggests a dif- 

 ference either in the variations of tlie blood supply or in the chemical stability 

 of the bone substance, or in both. The circulation is more complicated in a 

 third type bone than it is in a first or sec.ud, and therefore more subject to 

 structural deviations. 



