70 SMITHSONIAN CONTRIBUTIONS TO KNO\VLEDGE VOL. 35 



canal, about the size of a fiiie sewiny- needle, situated near the posterior wall. 

 The femur is therefore nearly solid bone. The cancellous center is composed 

 of fine lamella^ forming a meshwork extended from the internal circumferential 

 lamella'. Tlie meshes are filled with granular material, insoluble in ether or 

 chloroform. The lacunje are small, round, or oval and their eanaliculi are short, 

 bushy, and infrequent. Although the bird is a good flier its femur is practically 

 a solid bone. 



Type I-III, Ic. 



EIGHT FEMUR OF CHAUNA CKISTATA. CHESTED SCBEAMEE. NO. 2861, 



AMER. MUS. NAT. HIST. 



Pl. 6, Fig. 99. Syn. Tab. Ill 



Antero-posterior diameter of bone, 12.5 mm. ; lateral, 12 mm. 



Antero-posterior diameter of medullar}' canal, 10.5 mm. ; lateral, 10.5 nun. 



The medullary canal is empty. Medullary index, 277%. 



Structure. — Tlie section has the three divisions well marked. The external 

 circumferential lamella; form a narrow, distinct ring around the section. Their 

 lacunfE are long and the eanaliculi are straight. The central ring is composed 

 of Haversian systems of the (Ic) stage and of canals and fragments of lamellae. 

 The internal circumferential lamella; form a distinct ring around the medullary 

 canal. Their lacunee are long. 



Type III, Ic. 



LEFT FEMUR OF PANDION CAROLINENSIS. AMERICAN OSPREV. NO. 55, CR. MED. COLL. 



Pl. 6, Fig. 100. Syn. Tab. Ill 



Antero-posterior diameter of bone, 7.5 mm. ; lateral, 8 mm. 



Antero-posterior diameter of medullary canal, 6 mm.; lateral, 6.5 mm. 



The medullary canal is full. Medullary index, 188%. 



Structure. — The external circumferential lamellae are not distinct from the 

 miilerlying structure. The bone is composed of crude laminae which are fre- 

 quently interrupted by Haversian systems of the (Ic) differentiation, and 

 crossed at differing angles by vascular canals. In the posterior wall near the 

 mid-line is a cluster of small Haversian systems witli which tendon inter- 

 sections are blended. The lacunae of the lamina; are round and oval. 



Concentric laminae surround the medullary canal. They are frequently 

 crossed by short canals from the medullary canal. 



Type II-III, Ic. 



