NO. 3 COMPARATIVE HISTOLOGY OF FEMUK FOOTE 95 



Structvre. — The section is composed of lamelte with h)ii,i>' and narrow 

 lacunfc and hing, straight canalicnli. In the outer wall the lamellae are inter- 

 rupted by irregularly shaped whorls of oval and round lacunae closely packed 

 together in the bone substance. The canaliculi are short and bushy. In one of 

 these whorls a central canal apiiears and the whole figure resembles slightly 

 a crude Haversian system. A few large canals cross the section radially on 

 their way from the medullary canal to the external surface. The bone is 

 uniform. 



Type I. 



FEMUR OF MUS RATTUS. RAT. CR. MED. COLL. 



Pl. 9, Fig. 180. StxV. Tab. V 



Antero-posterior diameter of bone, 2.5 mm.; lateral, .3.5 mm. 



Antero-posterior diameter of the medullary canal, 1.5 mm. ; lateral, 2.5 mm. 



The medullary canal is full. Medullary index, 75%. 



Structure. — The section is composed of two concentric rings of about equal 

 width surrounding the medullary canal. The external ring is composed of 

 lamellje with long lacunae and long, branching canaliculi. Here and there cross 

 canals appear. The internal ring is composed of short lamellae, laminae, and a 

 few incomplete Haversian systems of the (lb) differentiation, separated by a 

 network of canals. The lacunae are oval and round and the canaliculi are bushy. 

 The internal circumferential lamellae are so blended with the other structures of 

 the internal ring that they are poorly defined. 



Type I-III, lb. 



LEFT FEMUR OF HETEROMYS. SPINY POCKET EAT. AMER. MUS. NAT. HIST. 



Pl. 9, Fig. 181. Syn. Tab. V 



Antero-posterior diameter of bone, 4.5 mm.; lateral, 2.5 mm. 



Antero-posterior diameter of medullary canal, 3.5 mm.; lateral, 2 mm. 



The medullary canal is full. Medullary index, 153%. 



Structure. — The anterior and inner walls are composed of lamellae with 

 long and oval lacunae and straight canaliculi, crossed radially by frequent 

 canals. The posterior wall is composed of rather crude Haversian systems 

 with oval lacunae and bushy canaliculi, and the ouler wall of lamcllic with oval 

 lacunae and bushy canaliculi, interrupted by crude lla\ersian syslciiis of (lie 

 (la) and (lb) differentiations and crossed by canals. The internal circum- 

 ferential lamelliP are not distinct. The bone shows but little differentiation of 

 structure. 



Type I-III, la, lb. 



