72 SMITHSONIAN CONTKIBUTIONS TO KNOWLEDGE VOL. 85 



medullary caual and form the dividing partition. Four large vascular canals 

 appear in the anterior wall and two or three in the posterior. Their lacunae 

 are long and oval with long and straight canaliculi. 

 Type I-III, Ic. 



FEMTK 0|- (iALLUS. DOMESTIC CHICKEN. OR. MED. COLL. 



Pl. 7, Fig. 10 1. Stn. Tab. Ill 



Antero-posterior diameter of bone, 9 mm. ; lateral, 9 mm. 



Antero-posterior diameter of medullary canal, 7 mm. ; lateral, 7 mm. 



The medullary canal is full. Medullary index, 153%. 



Structure. — Well marked external circumferential lamelhe with long, nar- 

 row lacunse and branching canaliculi surround the section. The central ring is 

 composed of irregularly shaped Haversian systems of the (Ic) differentiation. 

 At the posterior ridge they occupy the entire thickness of tlie wall of the bone 

 as far as the internal circumferential lamelL^. Interspersed between the sys- 

 tems are short lamellae. 



Internal circumferential lamellae completely surround the medullary canal. 

 Their lacunas are long and narrow and their canaliculi are bushy. 



Type I-III, Ic. 



FEMUR OF COKVUS AMERICANUS. CROW. CR. MED. COLL. 



Pl. 7, Fig. 105. Syn. Tab. Ill 



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



Antero-posterior diameter of medullary canal, 2.5 mm. ; lateral, 2 mm. 



The medullary canal is full. Medullary index, 70'/c. 



Structure. — External circumferential lamellae form a wide ring around the 

 bone. The laciuur are oval with bushy, connecting canaliculi. 



The central ring is composed of lamellae and irregular Haversian systems 

 of the (Ic) stage of development. There is very little difference in the struc- 

 ture of the various parts of the bone. 



Internal circumferential lamellae -form a narrow ring around the medullary 

 canal. Their lacunae are narrow and long and their canaliculi are long and 

 branching. 



Type I-III, Ic. 



FEMl'R OF ASIO WILSOXIANI'S. LONC-EARED OWL 



Pl. 7, Fig. lOii. Syn. Tah. Ill 



Antero-posterior diameter of bone, 8 mm.; lateral, 7 nun. 

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

 The medullary canal is full. IMedullary index, 178%. 



