NO. 3 



COMPARATIVE HISTOLOGY OF FEMUR FOOTE 



45 



Structure. — The section is surrounded by a wide ring of lamellae with long 

 lacunae and rather infrequent bushy canaliculi, interrupted by Haversian canals 

 of the (la) differentiation. The ring is widest in the lateral walls. The canals 

 appear in cross and oblique sections. Underneath this ring is a wide, central 

 ring composed of crude lamella' with oval lacunae and relatively few canaliculi, 

 enclosing large, irregularly shaped canals with surrounding, clear areas and 

 presenting a general concentric arrangement. A few internal circumferential 

 lamellae with long lacunae surround the medullary canal. Two large, open, round 

 spaces appear, one in the inner posterior wall and the other in the outer lateral 

 wall. The femur shows the three usual divisions — external circumferential 

 lamella?, central ring, internal circumferential lamellae and primitive Haversian 

 canals — all of which indicate slight advancement. Structural differentiation is 

 shown by the three divisions and primitive Haversian canals. 



Type I-HI, la. 



RIGHT FEMUR OF BUFO AGUA. BERMUDA TOAD. NO. 1113, AMER. MUS. NAT. HIST. 



Pl. 3, Fig. 32. Syn. Tab. I 



Antero-posterior diameter of bone, 5 mm. ; lateral, 3.5 mm. 

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

 The medullary canal is full. Medullary index, 39%. 



Structure. — The section is surrounded by a wide band of bone substance 

 with long, obliquely arranged lacunae and straight canaliculi, interrupted by 

 round, oval, and elongated filled canals around which are clear areas (la, dif- 

 ferentiation). Underneath this band is a wide central ring of lamellae with oval 

 lacunae and bushy canaliculi, interrupted by elongated and oval-filled canals 

 surrounded by clear areas of bone substance (la, differentiation). Fine cana- 

 liculi pass from these canals to adjacent lacunae. The canals mark the begin- 

 ning of Haversian systems. Around the medullary canal is a narrow ring of 

 lamellae with oval lacunae and bushy canaliculi. Threefold division. 



Type I-III, la. 



RIGHT FEMUR OF BUFO HALOPHILUS. NO. E 35 8, U. S. NAT. MUS. 



Pl. 3, Fig. 33. Syn. Tab. I 



Antero-posterior diameter of bone, 2 mm. ; lateral, 2 mm. 

 Antero-posterior diameter of medullary canal, 1.5 mm.; lateral, 1.5 mm. 

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



Structure. — The structure shows the three divisions. The external cir- 

 cumferential lamellae form a narrow boundary ring. The central ring consti- 

 tutes most all of the section, and is composed of lamellae with oval lacunae and 

 bushy canaliculi. In the anterior and posterior walls the ring is traversed by 



