NO. 3 COMPARATIVE HISTOLOGY OF FEMUK FOOTE 73 



Structure.— The external circnmfereutial lamella; surrouud the section. 

 Their lacunie are long, numerous, and have very fine, long caualiculi. Here and 

 there canals traverse the entire thickness of them all. 



The central ring is composed of irregularly shaped Haversian system of 

 the (Ic) stage of development, extending between which are numerous short 

 canals. The lacuufe are oval, numerous, and have bushy caualiculi. 



The internal circumferential lamellae form a thick, heavy ring around the 

 medullary canal. In the outer wall of the bone they tend to separate into 

 laminae. The whole ring of internal circumferential lamellae forms about one- 

 third of the thickness of the wall of the bone. It is traversed by many canals 

 extending from the medullary canal into the canals of the Haversian systems. 

 Their lacunae are long and numerous and their caualiculi are bushy. 



Type I-II-III, Ic. 



BIGHT FEMUR OF BERNICLA CANADENSIS. WILD GOOSE 



Pl. 7, Fig. 107. Syn. Tab. Ill 



Antero-posterior diameter of bone, 9 mm. ; lateral, 8.5 mm. 



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



The medullary canal is full. Medullary index, 378%. 



Structure. — The external circumferential lamellae surround the section. 

 Their lacunte are long and narrow and their caualiculi are rather few in num- 

 ber. At the posterior ridge are found many Haversian systems of the (Ic) 

 differentiation. The anterior wall of the bone is composed of similar Haversian 

 systems occupying the whole thickness of the wall between the external and 

 internal circumferential lamellje. The remainder of the bone shows quite dif- 

 ferent structures and arrangements in the different portions of the wall. 

 Lamina occupy the inner half of the wall, while Haversian systems of the (Ic) 

 stage of development occupy the outer half and are situated under the external 

 circumferential lamellae. 



The two lialves are well marked and distinct from each other. The lacunas 

 of the systems and laminjB are oval and their caualiculi are few and short. 

 The canals lietween the lamin* are irregular and branching. The internal 

 circumferential lamelhv are well developed. In the inner wall of the bone quite 

 large canals extend from the medullary canal through the laminae to the Ha- 

 versian canals between tlie lamina^. 



Type II-III, Ic. 



LEFT FEMUK OF LEPTOP'llLOS SP. STOKK. NO. 2827, AIM KH. .MPS. NAT. HIST. 



Pl. 7. Fm. 108. Syx. Tab. Ill 



Antero-posterior diameter of bone, 17 mm.; lateral, l.") mm. 

 Antero-posterior diameter of medullary canal, 14.5 mm.; lateral, 1.3.5 mm. 

 The medullary canal is empty. Medullary index, 327%. 



