190 SMITHSONIAN CONTBIBUTIONS TO KNOWLEDGE VOL. 35 



The central ring constitutes almost the whole thickness of the walls and is 

 composed of Haversian systems with some inter-Haversian lamellae. The sys- 

 tems are large, small, and irregnlar, and show some senile changes. There are 

 very few cross canals. Their lacunae are oval and narrow. 



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

 lary canal and in the anterior wall assume the form of cancellous bone. 



Type III, C, senile. 



RIGHT FEMUK OF A WHITE MALE, AGE 45. NO. 154, MED. DEFT. NORTHWESTERN UNIV. 



Pl. 30, Fig. 389. Syn. Tab. X 



Antero-posterior diameter of bone, 30 mm. ; lateral, 29 mm. 



Antero-posterior diameter of medullary canal, 15 mm. ; lateral, 14 mm. 



The medullary canal is full. Medullary index, 26%. 



Structure. — The external circumferential lamellae are fragmentary. The 

 central ring is composed of Haversian systems, which, in tlie inner wall, alter- 

 nate with concentric laminae. Many systems are senile. 



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

 lary canal. 



Type III, C, senile. 



LEFT FEMUR OF A WHITE MALE. NO. 146, MED. DEFT. NORTHWESTERN UNIV. 



PL. 30, Fig. 390. Syn. Tab. X 



Antero-posterior diameter of bone, 28 mm.; lateral, 24 mm. 



Antero-posterior diameter of medullary canal, 13 mm. ; lateral, 10 mm. 



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



Structure. — The external circumferential lamelte are fragmentary. Half 

 systems frequently occur on the external border of the section. The central 

 ring forms practically all of the bone and is composed of irregularly shaped 

 Haversian systems. Senile changes are marked. The lacunas are oval and long 

 and the canaliculi are bushy and straight. The internal circumferential lamellae 

 are fragmentary. 



Type III, C, senile. 



LEFT FEMUK OF A WHITE MALE, ACK GO. NO. 159, MED. UEF'i'. NORTHWESTERN UNIV. 



I'L. 30, KiG. 391. Syn. Tab. X 



Antero-posterior diameter of bone, 32 aim.; lateral, 31.5 mm. 

 Antero-posterior diameter of medullary canal, 17.5 mm.; lateral, 18 nnn. 

 The medullary canal is full. Medullary index, 45%.. 



Structure. — The external circumferential lamellae are fragmentary. The 

 central ring is composed of Haversian systems showing many senile elianges. 



