68 



SMITHSONIAN CONTBIBUTIONS TO KNOWLEDGE 



VOL. 35 



LEFT FEMUR OF STRUTHIO. OSTRICH. AMER. MUS. NAT. HIST. 



Pl. 6, Pig. 94. Syn. Tab. Ill 



Antero-posterior diameter of bone, 54 mm. ; lateral, 40 mm. 



Antero-posterior diameter of medullary canal, 47 mm. ; lateral, 32 mm. 



The medullary canal is empty. Medullary index, 240%. 



Structure. — The bone is large, thin-walled, and light. The section is com- 

 posed of incomplete, concentric, short and long laminae, crossed by numerous 

 canals, and interrupted by many Haversian systems of the (Ic) stage of dif- 

 ferentiation. The posterior ridges are composed mostly of similar Haversian 

 systems. The central zones of these systems are composed of lamellae with 

 round lacunae and short, bushy canaliculi, while their external zones, much nar- 

 rower, consist of lamellae with long, narrow lacunae and straight canaliculi. 



Type II-III, Ic. 



HAVERSIAN SYSTEM OF THE OSTRICH 



Pl. G, Fig. 95. Syn. Tab. Ill 



An Haversian system from the posterior wall of the femur of an ostrich 

 (fig. 94) is enlarged in order to show developmental stages. 



The system consists of a central and peripheral portion. The central 

 portion is composed of bone substance with round lacunae and branching cana- 

 liculi forming a delicate canalicular network around the Haversian canal. The 

 peripheral portion is composed of long, narrow lacunae with straight canaliculi 

 situated in and between lamellae and arranged concentrically around the central 

 portion. The central portion suggests an early development by its round 

 lacunae and close proximity to the circulation of the Haversian canal, while 

 the peripheral portion suggests a later and more complete development by its 

 long, narrow lacunae and removal from the Haversian canal. 



LEFT FEMUR OF PHASIANUS TORQUATUS. CHINESE PHEASANT. CR. MED. COLL. 



Pl. 6, Fig. 95J. Syn. Tab. Ill 



Antero-posterior diameter of bone, 6 mm.; lateral, 6 mm. 

 Antero-posterior diameter of medullary canal, 4.5 mm. ; lateral, 4.5 mm. 

 The medullary canal is empty. Medullary index, 129%. 



Structure. — The section is composed of crude, short laminae interrupted 

 by a few Haversian systems of the (Ic) differentiation. The lacunae are oval 

 and the canaliculi are short and bushy. Internal circumferential lamellae partly 

 surround the medullary canal. 



Type II, Ic. 



