NO. 3 COMPARATIVE HISTOLOGY OF FEMUR FOOTE 145 



FEMUR OF CASIS. SMALL GREY FOX. OR. MED. COLL. 



Pl. 20, Fig. 291. Syn. Tab. Vll 



Antero-posterior diameter of bone, 8 mm.; lateral, 9 mm. 



Antero-posterior diameter of medullary canal, 5 mm.; lateral, 6.5 mm. 



The medullary canal is full. Medullary index, 80%. 



Structure. — A ring of external circumferential lamellfe and laniinEe, inter- 

 rupted by Haversian systems of the (la) differentiation, surrounds the bone. 

 In the outer wall the lamellar ring is distinct, but in the inner wall it widens 

 and separates into laminae which occupy the whole thickness of the wall. The 

 laminfe are short and are separated and crossed by intercommunicating canals. 

 On the inner lateral side of the posterior wall is a ridge and the laminae from 

 the inner wall reach the surface at this point and appear to interdigitate with 

 inward extensions from the periosteum. The lacunje are long and narrow; tlie 

 canaliculi are long and branching. 



The central ring is composed of a wide crescent of well developed Ha- 

 versian systems, the horns of which begin a short distance apart in the innert 

 wall, while the widest part of the body occupies the outer wall. The systems 

 are small and large, regular and irregular in shape. Their lamellae are well 

 defined; their lacunae are long and narrow; and their canaliculi are branching. 

 Their Haversian canals frequently communicate. 



Around a portion of the medullary canal is a border of Haversian systems. 

 The internal circumferential lamellag form an incomplete ring around the medul- 

 lary canal. 



Type I-II-III, la, C. 



LEFT FEMUK OF TAXXDEA AMERICANA. AMERICAN BADGER. AMER. MUS. NAT. HIST. 



Pl. 20, Fig. 292. Syn. Tab. VII 



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



Antero-posterior diameter of medullary canal, 4 nun. : latoral, 4 mm. 



The medullary canal is full. Medullary index, 40%. 



Structure. — The section is surrounded in the anterior and lateral wall by 

 external circumferential lamellaj. In the posterior wall tlie lamella' are ar- 

 ranged obliquely. Under the lamella? is a narrow crescent of small, well de- 

 veloped Haversian systems. Under the ring of systems is a wide ring of 

 laminae which in the posterior wall are arranged obliquely from the medullary 

 canal. The canals between the lamina are wide and brandling. The lacuna 

 are oval and long. 



Type I-II-III, C. 



