NO. 3 COMPARATIVE HISTOLOGY OF FEMUR FOOTE 125 



The bone exhibits a mueh greater lamellar structure thau the femur of 

 the two-toed sloth. It is quite different in shape. Senility is marked. 

 Type I-III, la, C, senile. 



EIGHT FEMUR OF CASTOR CANADENSIS. BEAVER. NO. 10005, U. S. NAT. MUS. 



Pl. 16, Fig. 250. Syn. Tab. VI 



Antero-posterior diameter of bone, 25 mm.; lateral, 11 mm. 



Antero-posterior diameter of medullary canal, 6 mm. ; lateral, 4 mm. 



The medullary canal is full. Medullary index, 10%. 



Structure. — The section has a long posterior ridge, which accounts for the 

 long antero-posterior and short lateral measurements. The section is sur- 

 rounded by a lamellar and laminar band of varying widths, interrupted by 

 Haversian canals of the (la) differentiation and crossed liy frequent vascular 

 canals. The lacunae are oval and long and the canaliculi are straight. 



Underneath the lamella; is a narrow band of irregular Haversian systems. 

 The systems are large and small, but very well developed. They are quite 

 irregular in shape. Their canals frequently unite. The central part of the 

 ridge is composed of large Haversian systems, poorly developed and united by 

 vascular canals. The internal circumferential lamellae assume the form of can- 

 cellous bone around the medullary canal. 



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



LEFT FEMUR OF FELIS. LEOPARD. NO. 35349, AMER. MUS. NAT. HIST. 



Pl. 16, Pig. 251. Syn. Tab. VI 



Antero-posterior diameter of bone, 18 mm.; lateral, 17 mm. 



Antero-posterior diameter of medullary canal, 10 mm.; lateral, 9 mm. 



The medullary canal is full. Medullary index, 37%. 



Structure. — The section has three divisions. A wide band of lamellae and 

 Haversian systems surrounds the bone. It is widest in the inner wall. The 

 systems are numerous and do not appear to have any definite plan of arrange- 

 ment. The lacuniE are long and the canaliculi are straight. The central ring, 

 irregular in width, is composed of well developed HaN'ersian systems with little 

 inter-Haversian lamellfe. The internal circumferential lamelhE form a frag- 

 mentary ring around tlie medulhii-y canal. Many spaces (icciir which a|>p('ar to 

 be the result of the disappcai'ancc of Haversian systems. Senile cliaiiges are 

 frequent. 



Type I-III, C, senile. 



