NO. 3 



COMPARATIVE HISTOLOGY OK FEMUE FOOTB 



201 



Structure. — The section is surrounded by a band of lamellae and lamina?. In 

 the anterior and inner wall the band is lamellar and perforated by numerous 

 canals of the (la) differentiation. In the outer and posterior wall the band is 

 laminar and interrupted by elongated Haversian systems of the (lb) formation. 



The central ring is irregular. In the outer wall it is thick and composed 

 of well developed Haversian systems ; in the antero-inner lateral wall it is 

 thin; and in the posterior inner lateral it is almost entirely absent. 



Internal circumferential lamellae form a narrow cancellous ring around 

 the medullary canal. The lamellae are separated into laminae in the inner wall. 



Type I-II-iri, la, lb, C. 



LEFT FEMUR OF A WHITE MALE. NO. 98, CR. MED. COLL. 



Pl. 33, Fig. 417. Syn. Tab. XI 



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

 Antero-posterior diameter of medullary canal, 17 mm. ; lateral, 15 mm. 

 The medullary canal is full. Medullary index, 39%. 



Structure. — External circumferential lamellae and laminae surround the sec- 

 tion. In the inner wall are two rows of elongated Haversian systems extending 

 in a concentric direction from the external laminae to the medullary surface of 

 the anterior wall. The central ring of Haversian systems constitutes almost the 

 entire thickness of the wall of the bone. The inner wall shows the borders of a 

 wide external crescent composed of very much flattened Haversian systems. 



The Haversian systems are large, small, and irregular in shape. Nearly 

 one-half of them in the outer and a few in the inner wall show senile changes. 

 The various stages of senility are well marked in this bone. In the early stage 

 the lamellae of the Haversian systems are prominent. The organic portion of 

 the lamellae seems to separate from the inorganic and the mineral salts begin 

 to appear as granules in the lamellae around the Haversian canals. In this 

 stage the systems appear brown with sharply defined lamellae. In the next stage 

 the mineral deposit is heavy and the systems are black. Here and there a sys- 

 tem can be seen in the last stage. The lamellae around the Haversian canal 

 are absorbed and little by little the Haversian canal widens until a narrow 

 black ring is all that remains of the system, or the entire system disappears. 

 The inorganic salts are deposited in the Haversian canals (pl. 34, figs. 424-426). 

 After this manner the bone becomes light and the walls become thin as the 

 process extends outward from the medullary canal. The internal circumferen- 

 tial lamellae appear in fragments. 



Type I-II-III, C, senile. 



