NO. 3 COMPARATIVE HISTOLOGY OF FEMUR FOOTE 117 



The central ring is incomplete, occupying the posterior, inner, and anterior 

 walls. It is composed of well developed Haversian systems, crossed in the 

 anterior wall by an extension from the external lamellae. It is wide in the 

 posterior wall and gradually narrows as it passes around the lateral into the 

 anterior wall. 



Around the medullary canal is a well defined ring of internal circum- 

 ferential lamella;. Numerous large canals cross the ring to communicate with 

 canals within the center of the bone. The lacunae are long and canaliculi long 

 and branched. 



Type I-III, lb, C. 



FEMUR OF MEPHITIS MEPHITICA. SKUNK. CR. MED. COLL. 



Pl. 14, Fig. 233. Syn. Tab. VI 



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



Antero-posterior diameter of medullaiy canal, 3.5 mm.; lateral, 4 mm. 



The medullary canal is full. Medullary index, 127%. 



Structure.- — The section is composed of lamellae with long lacunae and 

 straight and bushy canaliculi, frequently interrupted by irregularly shaped Ha- 

 versian systems and canals. Some of the systems are round, some oval, and 

 some have long, wide, straight, or curved canals. In some situations they are 

 concentric. As a whole, they are well developed. There is no well defined 

 central ring nor internal circumferential lamellae. 



Type I-III, C. 



FEMUR OF PUTORTUS VISON. MINK. 



Pl. 14, Fig. 234. Syn. Tab. VI 



Antero-posterior diameter of bone, 3.5 mm.; lateral, 4.5 ram. 



Antero-posterior diameter of medullary canal, 1.5 mm.; lateral, 2 mm. 



The medullary canal is full. Medullary index, 23 7^- 



Structure. — The anterior wall is composed of lamelte which form its entire 

 thickness. The lamellae then form an irregularly shaped, complete ring around 

 the medullary canal. Numerous canals pass across this ring, incompletely or 

 completely, on their way from the medullary canal to small canals of the in- 

 terior. The lacunae are long and narrow and their canaliculi are long and 

 branching. 



The Haversian systems are absent at the widest lamellar point of the an- 

 terior wall. They then begin to appear in single file, gradually increase in thick- 

 ness to the posterior wall, and diminish again as they approach the anterior 

 wall. In this manner they form an irregular long crescent enclosed within 



