NO. 3 



COMPARATIVE HISTOLOGY OF FEMUR FOOTE 



69 



RIGHT FEMUR OF DROM.EUS NOV^S HOLLANDLE. EMU. NO. 2916, AMER. MUS. NAT. HIST. 



Pl. 6, Pig. 96. Syn. Tab. Ill 



Antero-posterior diameter of bone, 30 mm. ; lateral, 26 mm. 

 Antero-posterior diameter of medullary canal, 22 mm. ; lateral, 19.5 mm. 

 Medullary index, 122%. 



Structure. — The section is composed, for the most part, of a background 

 of short laminae separated by short concentric canals in which are scattering 

 Haversian systems of the (Ic) differentiation. In the outer wall a threefold 

 division is present — external circumferential lamina?, central ring, and internal 

 circumferential lamellae. 



The central ring is composed of Haversian systems, many of which are 

 arranged in a peculiar manner. They occur in groups of two to eight, enclosed 

 within an envelope of laminae resembling cross-sections of cables. The systems 

 are of the (Ic) differentiation. This is the only bone in which this arrange- 

 ment has been seen. 



Type II-III, Ic, 



FEMUR OF ANAS BOSCAS. MALLARD DUCK. OR. MED. COLL. 



Pl. 6, Fig. 97. Syn. Tab. Ill 



Antero-posterior diameter of bone, 4.5 mm. ; lateral, 6.5 mm. 



Antero-posterior diameter of medullary canal, 3.5 mm. ; lateral, 5 mm. 



The medullary canal is empty. Medullary index, 141%. 



Structure. — The section is composed of crude laminae arranged concen- 

 trically and interrupted by rather small and poorly developed Haversian sys- 

 tems. The two posterior ridges have groups of the (Ic) differentiation. 



Type II-III, Ic. 



FEMUR OF EMBERIZA CITRINELLA. YELLOW-HAMMER. CR. MED. COLL. 



Pl. 6, Fig. 98. Syn. Tab. Ill 



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

 Antero-posterior and lateral diameters of medullary canals, 0. 

 The medullary canal is full and situated close to the posterior wall. Medul- 

 lary index, 0. 



Structure. — The section is surrounded by external circumferential lamellae, 

 within which are a few Haversian systems of the (Ic) differentiation. Large 

 canals extend transversely across the walls of the bone, communicating with the 

 meshes of the central bone structure. 



The central portion of the bone, usually occupied by the medullary canal, 

 is composed of a fine cancellous bone with the exception of a small medullary 



