204 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 35 



Figure 426 shows the last stage. The lamellae have nearly all disappeared, 

 and a narrow black ring only remains. The Haversian canal is large and irregu- 

 lar in shape. The medullary canal is very much increased in size and the bone 

 is light in weight. 



Senile changes are more frequent around the medullary canal than else- 

 where, although they may occur in any part of the bone. 



As the lameUsB around the Haversian canals become more and more opaque 

 with inorganic salts they gradually disintegrate, the inorganic matter enters 

 the blood vessels and is carried into the general circulation to be removed from 

 the body or deposited in the degenerating wall of blood vessels. 



EIGHT FEMUB OF A WHITE MALE (cONVICT). NO. 2, MED. DEPT. NEBRASKA UNIV. 



Pl. 35, Fig. 428. Syn. Tab. XI 



Antero-posterior diameter of bone, 32 mm. ; lateral, 27.5 mm. 



Antero-posterior diameter of medullary canal, 15 mm.; lateral, 10 mm. 



The medullary canal is full. Medullary index, 21%. 



Structure. — A narrow band of external circumferential lamellae surrounds 

 the section. 



The central ring is composed of large, small, and variously shaped Ha- 

 versian systems with relatively small Haversian canals. On account of the 

 small canals the Haversian systems have tliick walls. Many of the canals are 

 situated eccentrically. Scattered throughout the wall of the section are many 

 Haversian systems in various stages of senility. In some, the two or three 

 lamellse around the Haversian canal are involved ; in others, half of the system is 

 senile; and in others, the whole system is black with mineral precipitation. In 

 the posterior inner wall a few elliptical Haversian systems occur. 



Internal circumferential lamelte surround the meduUary canal. The lacunae 

 of the section are generally oval. 



Type III, C, senile. 



EIGHT FEMUE OF A WHITE MALE (cONVICt). NO. 3, MED. DEPT. NEBRASKA UNIV. 



Pl. 35, Fig. 429. Syn. Tab. XI 



Antero-posterior diameter of bone, 26.5 mm. ; lateral, 25 mm. 



Antero-posterior diameter of medullary canal, 15 mm.; lateral, 12 mm. 



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



Structure. — The external circumferential lamellje are fragmentary. The 

 central ring is composed of variously shaped, large and small Haversian sys- 

 tems with no inter-Haversiau lamellae. Some of the systems are well developed ; 

 some have small Haversian canals ; some show earl}^ stages of senility ; some 



