NO. 3 COMPARATIVE HISTOLOGY OF FEMUR FOOTE 67 



smaller canals extending from both surfaces of the bone. Tlie laminae are com- 

 posed of lamelliB, between which are oval lacuna? with short, bushy eanaliculi. 

 Around the medullary canal the internal circumferential lamellas are not dis- 

 tinct from the adjoining laminiB. 



As the femur of the domestic turkey was the first bone to suggest variation 

 in bone type, a number of turkey femora were examined. It was found that 

 they were all second type with Haversian systems of the (la) and (Ic) stages 

 of development. The turkeys of greatest weight had the most Haversian sys- 

 tems. A turkey of 32 pounds weight (pi. 6, fig. 91|) had more systems than one 

 of 14, 16, or 18 pounds, and the systems were distributed over a greater area 

 in the different walls of the bone. 



Type II-III, la, Ic. 



LEFT FEMUR OF DENDRAGAPUS OBSCURUS. GROUSE. CR. MED. COLL. 



Pl. 6, Fig. 92. Stn. Tab. Ill 



Antero-posterior diameter of bone, 5 mm. ; lateral, 5.5 mm. 



Antero-posterior diameter of medullary canal, 4 mm.; lateral, 5 mm. 



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



Structure. — The bone, with the exception of a narrow ring of internal cir- 

 cumferential lamelte, is composed of short, concentric lamiuje, separated by 

 wide canals. Each lamina is composed of lamellae, with long, narrow or oval 

 lacunae and long, branching or bushy eanaliculi. TJie canals freely communi- 

 cate with each other across the lamina. In the anterior wall (middle portion) 

 is a slight prominence or ridge, consisting of poorly developed Haversian sys- 

 tems, situated close to the external surface. In the posterior wall are two 

 ridges separated by a concave intermediate wall of bone. A single, ]K>()r]y 

 developed Haversian system is found at the apex of each ridge, around wliich 

 are collections of oval lacuna;, with short, bushy canalicidi. Close to the internal 

 circumferential lamellae are a few Haversian systems of a crude type. 



Internal circumferential lamellae surround the medullary canal. Their 

 lacuna are long and narrow. 



Type II. 



LEFT FEMUR OF RHEA AMERICANA. RHEA. NO. 2875, AMER. MUS. N.\T. HIST. 



Pl. 6, Fig. 93. Syx. Tab. Ill 



Antero-posterior diameter of bone, 25.5 mm.; lateral, 20.5 mm. 



Antero-posterior diameter of medullary canal, 19 mm.; lateral, 15 mm. 



The medullary canal is full. Medullary index, 120%. 



Structure. — The section is composed of concentric laminae, separated and 

 crossed by numerous canals, and, here and there, interrupted by small Ha- 

 versian systems of the (Tc) differentiation. 



Type II-III, Ic. 



