NO. 3 COMPARATIVE HISTOLOGY OF FEMUR FOOTE 57 



clear areas of bone substance. Oval lacunte are arranged concentrically around 

 the boundaries of these areas and bushy canaliculi pass from the laeunfc to the 

 canals. The lamiiife are much better develojjed than the Plaversian systems 

 which have reached the (lb) differentiation. The posterior wall is composed 

 of bone substance with round lacunae and bushy canaliculi arranged as a crude 

 cancellous bone and merges into tlie cancellous bone of tlie medullary canal. 

 Type I-II-III, la, lb. 



RIGHT FEMUR OF TRIONYX SPINIB'ER. SOFT-SHELLED TURTLE. NO. 2325, 



AMER. MUS. NAT. HIST. 



Pl. 4, Fig. 67. Syn. Tab. II 



Antero-posterior diameter of bone, 3.5 mm.; lateral, 5.5 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 lamellaB with oval lacuna? 

 and bushy canaliculi. It is interrupted by Haversian canals of the (la) dif- 

 ferentiation. In the posterior wall Jiere and there an Haversian system appears 

 in the (lb) stage of advancement. Cancellous bone occupies the central canal 

 of the bone and is derived, by extension, from the enclosing lamellar ring. The 

 walls of the cancellous meshes are composed of lamella with oval and long 

 lacunae and straight canaliculi. There is no individual medullary canal. 



Type I-III, la, lb. 



RIGHT FEMUR OF CINOSTERNUM PENNSYLVANICUM. MUD TURTLE. 

 AMER. MUS. NAT. HIST. 



Pl. 4, Fig. 68. Syn. Tab. II 



Antero-posterior diameter of bone, 3 mm.; lateral, 3.5 mm. 



Antero-posterior diameter of medullary canal — cancellous bone. 



The medullary canal "is full. Medullary index, 0. 



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

 oval lacuna? and bushy canaliculi, from which is derived the cancellous bone 

 which fills the medullary canal. A few Haversian systems of the (lb) dif- 

 ferentiation are found in the posterior wall. 



Type I-III, lb. 



RIGHT FEMUR OF CHELOPUS GUTTATUS. SPOTTED TURTLE. AMER. MUS. NAT. HIST. 



Pl. 4, Fig. 69. 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. 



