NO. 3 



COMPARATIVE HISTOLOGY OF FEMUR FOOTE 



57 



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

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

 canals. The lamina? are much better developed than the Haversian systems 

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

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

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

 Type I-II-III, la, lb. 



RIGHT FEMUR OF TRIONYX SPINIFER. 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 lamella? with oval lacunas 

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

 ferentiation. In the posterior wall here 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 lamellas with oval and long 

 lacunas 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 lamellas with 

 oval lacunas 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. 



