92 SMITHSONIAN CONTKIBUTIDXS TO KNOAVLEDGE VOL. 35 



LEFT FEMUR OF CAVIA CUTLERI. GUINEA PIG. AMEK. MUS. NAT. HIST. 



Ph. 9, Fic. 171. Svx. Tai;. V 



Antero-posteriof diameter of hone, 6 mm.; lateral, 4 mm. 



Antero-posterior diameter of medullary canal, 4 mm.: lateral. ."> mm. 



The medullary raual is full. Medullary index, lOU'/. 



Structure. — The three divisions are plainly marked. The external eiroum- 

 ferential lamella with long- lacuna^ and straight eanaliculi form a narrow ring 

 around the hone. The central ring consists of hasie bone substance with roimd 

 and oval lacuna? and bushy canaliculi, interrupted by poorly developed Ha- 

 versian systems of the (la) differentiation and crossed by radiating canals. In 

 the posterior wall the ring consists of crude Haversian systems between which 

 is bone substance with oval lacunfe and bushy canaliculi. 



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

 lary canal. The bone shows a threefold division. 



Type I-III, la. 



LEFT FEMUR OF SCAI_,OPUS AQU.\TICUS. MOLE. AMER. MUS. NAT. HIST. 



Pl. 9, Fig. 172. Syn. Tab. V 



Antero-posterior diameter of bone, 1.5 mm. ; lateral, 1.5 mm. 



Antero-posterior diameter of medullary canal, 1 mm.; lateral, 1 mm. 



The medullary canal is full. Medullary index, 80%. 



Structure. — The section is composed of lamellae with long and oval lacuna; 

 and straight canaliculi, partially separated into two equal, concentric rings by 

 concentric, branching canals and crossed at various angles by radiating canals. 

 In the posterior wall the lamellae are crude Haversian systems of the (lb) 

 differentiation. 



Type I-III, lb. 



RIGHT FEMUR OF SOREX. SHREW. AMER. MUS. NAT. HIST. 



PL. 9, Fig. l^S. Syx. Tab. V 



Antero-posterior diameter of bone, 3 mm. ; lateral, 3.3 mm. 



Antero-posterior diameter of medullary canal, 1.2 mm.; lateral. 1.5 mm. 



The medullary canal is full. Medullary index, 22%. 



Structure. — The section is composed of bone substance with oval lacuiuB 

 and bushy canaliculi, freciuently interrupted by primitive Haversian systems of 

 the (II)) differentiation and crossed by canals. In some places fragments of 

 external circumferciitial lamelhr appear. In I lie yioslcrioi- wall is a group of 

 oval lacunae witii short, bushy canaliculi. 



The bone shows but little diffei-entiation of structure. It is uniformly of 

 an early differentiation. 



Type I-III, lb. 



