58 



SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE 



VOL. 35 



Structure. — The section is surrounded by a narrow ring of lamellae with 

 oval lacunae and bushy canaliculi, interrupted by a few Haversian canals of 

 the (la) differentiation. From the under surface of this ring is derived a 

 cancellous bone which entirely tills the medullary canal. The walls of the 

 meshes are composed of lamellse with oval lacunae and bushy canaliculi. In the 

 posterior wall are a few Haversian systems of the (lb) stage of development. 



Type I-III, la, lb. 



LEFT FEMUR OF CHRYSEMYS PICTA. PAINTED TURTLE. AMER. MUS. NAT. HIST. 



Pl. 4, Fig. 70. Syn. Tab. II 



Antero-posterior diameter of bone, 2.5 mm. ; lateral, 4 mm. 

 Antero-posterior diameter of medullary canal — cancellous bone. 

 The medullary canal is full. Medullary index, 0. 



Structure. — The section is surrounded by a ring of lamellae with oval 

 lacunae and bushy canaliculi, interrupted by a few Haversian canals of the 

 (la) differentiation. Haversian systems of the (lb) stage of development are 

 found in the posterior wall. From the lamellar ring is derived the cancellous 

 bone which occupies the whole medullary canal. 



Type I-III, la, lb. 



RIGHT FEMUR OF AROMOCHELYS ODOBATUS. MUSK TURTLE. AMER. MUS. NAT. HIST. 



Pl. 4, Fig. 71. Syn. Tab. II 



Antero-posterior diameter of bone, 1.8 mm. ; lateral, 1.4 mm. 

 Antero-posterior diameter of medullary canal, 0.3 mm. ; lateral, 0.3 mm. 

 The medullary canal is full. Medullary index, 4%. 



Structure. — The section is surrounded by a band of lamellae of various 

 widths. The lacunae are long and their canaliculi are long and straight. Under- 

 neath this is a central ring of lamellae with oval lacunae and bushy canaliculi. 

 In this ring are several Haversian systems of the (lb) differentiation forming 

 a circular row around the medullary canal. 



Around the medullary canal is a ring of internal circumferential lamellae 

 with Ions lacuna? and straight canaliculi. The bone shows the outlines of the 

 three divisions — external and internal circumferential lamellae and the central 

 ring of lamellae with Haversian systems. 



Type I-III, lb. 



right femur of pseudemys floridana. no. 28417, u. s. NAT. mus. 



Pl. 4, Fig. 72. Syn. Tab. II 



Antero-posterior diameter of bone, 4 mm. ; lateral, 3 mm. 

 Antero-posterior diameter of medullary canal — cancellous bone. 

 Medullary index, 0. 



