186 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 35 



Structure. — The external circumferential lamella appear in fragments. 

 The central ring is composed of Haversian systems and constitutes almost the 

 entire wall of the bone. Many systems are senile. They reach the external 

 surface between the lamellar fragTuents and form the posterior ridge. They are 

 large, small, and irregular in shape and frequently communicate by canals. 

 Their lacnnic are narrow and oval. Around the internal circumferential lamella" 

 the systems show senile changes. There is very little inter-Haversian structure. 



Tlie internal circumferential lamellae form a very narrow ring around the 

 medullary canal. 



Type III, C, senile. 



LEFT FEMUR OF A WHITE MALE. NO. 96, CR. MED. COLL. 



Pl. 29, Fig. 378. Syn. Tab. X 



Antero-posterior diameter of bone, 29.5 mm.; lateral, 30 mm. 



Antero-posterior diameter of medullary canal, 14.5 mm.; lateral, 12 mm. 



The medullary canal is full. ^Medullary index, 24%. 



Structure. — A few fragments of the external circumferential lamella? ap- 

 pear here and there around the surface of the bone. The central ring of Ha- 

 versian systems constitutes almost entirely the whole section. 



There are some inter-Haversian lamellae which are the remains of the 

 laminar and lamellar structures seen in lower bones. The systems are large, 

 small, and irregular in shape and frequently communicate by canals. Some of 

 them show senile changes. On the whole, they are well developed. 



The internal circumferential lamellae form a very narrow, irregular ring 

 around the medullary canal. It is displaced at intervals by Haversian systems 

 of the central ring. 



Type III, C, senile. 



LEFT FEMUR OF A WHITE MALE, AGE 45. NO. 168, MED. DEPT. NORTHWESTERN UNIV. 



Pl. 29, Fig. 379. Syn. Tab. X 



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



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



The medullary canal is full. Medullary index, 40%. 



Structure. — The external circumferential lamellae are fragmentary. The 

 central ring is composed of large, small, and irregularly shaped Haversian 

 systems, many of which show senile changes. The internal circumferential 

 lamellae form a narrow fragmentary ring around the medullary canal. 



Type III, C, senile. 



