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SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE 



VOL. 35 



lamellae form the whole thickness of the anterior wall with the exception of 

 the internal circumferential lamellae. 



The internal circumferential lamellae, with a long, narrow crescent of Ha- 

 versian systems of the (lb) differentiation, especially in the posterior and 

 adjacent lateral wall, surround the medullary canal. 



Type I III, la, lb. 



LEFT FEMUR OF MANIS. SCALY ANT-EATER. AMER. MUS. NAT. HIST. 



Pl. 10, Fig. 193. Syn. Tab. V 



Antero-posterior diameter of bone, 7.5 mm. ; lateral, 11 mm. 

 Antero-posterior diameter of medullary canal, 5 mm. ; lateral, 7 mm. 

 The medullary canal is full. Medullary index, 74%. 



Structure. — The three divisions appear indistinctly marked. The external 

 circumferential lamellae with long lacunae and straight canaliculi form a wide 

 band around the section. They are interrupted by crude Haversian systems 

 of the (la) differentiation and crossed by canals which assume a radial direc- 

 tion, Under this band is a narrow ring of lamellae with oval lacunae and bushy 

 canaliculi. Beneath this again is a narrow ring of Haversian systems of the 

 (lb) differentiation. The lacunae are oval and long and the canaliculi are bushy. 



Internal circumferential lamellae form a narrow ring around the medullary 

 canal. Their lacunae are oval. In the outer wall tendon insertions and crude 

 systems are found. Threefold division. 



Type I-III, la, lb. 



RIGHT FEMUR OF PROCAVTA CAPENSIS. CONEY. NO. 35326, AMER. MUS. NAT. HIST. 



Pl. 10, Pig. 191. Syn. Tab. V 



Antero-posterior diameter of bone, 7.5 mm. ; lateral, 5 mm. 

 Antero-posterior diameter of medullary canal, 3 mm. ; lateral, 2.5 mm. 

 The medullary canal is full. Medullary index, 25%. 



Structure. — The external circumferential lamellae form a narrow boundary 

 of the posterior wall and then gradually widen to form the whole of the anterior 

 wall. They are interrupted by Haversian systems of the (la) differentiation. 



Their lacunae are long and their canaliculi are straight. In the posterior 

 half of the section the central ring borders the medullary surface of the pos- 

 terior and inner wall and is discontinued as it reaches the anterior wall. It is 

 composed of well developed Haversian systems. Internal circumferential la- 

 mellae form a broken ring around the medullary canal. 



Type I-III la, C. 



