NO. 3 COMPARATIVE HISTOLOGY OF FEMUR FOOTE 203 



versiau systems with considerable iuter-Haversian lamellae. As the band of the 

 inner wall approaches the anterior it is entirely displaced by Haversian sys- 

 tems, while the band of the outer wall is displaced about the mid-lateral region. 

 The central ring, therefore, is irreg-ular in shape and position. It is comjaosed 

 of well developed Haversian systems. 



The internal circumferential lamellae form a narrow ring around the medul- 

 lary canal. 



Type I-III, C. 



RIGHT FEMUR OF A WHITE MALE, AGE 40. NO. 142, MED. DEPT. NORTHWESTERN UNIV. 



Pl. 34, Fig. 421. Stn. Tab. XI 



Antero-posterior diameter of bone, 30 mm. ; lateral, 27.5 mm. 



Antero-posterior diameter of medullary canal, 13 mm. ; lateral, 11.5 mm. 



The medullary canal is full. Medullar}' index, 22%. 



Structure. — Beginning on both sides of the posterior ridge and extending 

 around the section is an enclosing band of varying widths comijosed of lamellae, 

 interrupted by small Haversian systems of the (la) differentiation. Tlie band 

 is widest in the outer and anterior wall. 



Underneath this band is a wide central ring of well developed Haversian 

 systems. They vary in size and present some senile changes around the medul- 

 lary canal. 



The internal circumferential lamelte form a narrow ring around the medul- 

 lary canal. The bone units are well developed. 



Type I-III, la, C, senile. 



haversian systems showing stages of senility 

 Pl. 34, Figs. 433-24-25-36 



These systems were taken from figure 417 and enlarged. Figiire 423 shows 

 an Haversian system before senile changes are visible. It is composed of a 

 number of concentric lamellae with serrated edges united by cement. The lacunae 

 are long and narrow and are situated either between the lamellte or witliin them. 

 There does not seem to be any regularity in the arrangement. 



Figure 424 shows an early stage of senility. In this Haversian system 

 there is a deposit of opaque granules in the lamellae around the Haversian canal. 

 The density of the granules diminishes from the canal toward the periphery. 



Figure 425 shows a later stage. The density has increased and expanded. 

 The central lamellae have dropped out and the Haversian canal is larger. The 

 whole system is more or less involved. In the external portion the granules 

 are brown and the lamellae are somewhat dim. The central ring is black. 



