96 



SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE 



VOL. 35 



RIGHT FEMUR OF MYOGALE MOSCHATA. DESMAN. CR. MED. COLL. 



Pl. 9, Fig. 182. Syn. Tab. V 



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



Antero-posterior diameter of medullary canal, 2.5 mm. ; lateral, 3 mm. 



Medullary canal has no contents. Medullary index, 30%. 



Structure. — The inner wall of the bone is extended in the form of a ridge, 

 which is composed of a network of lamina? and canals running transversely and 

 occupying the outer four-fifths of the ridge. Each lamina is composed of lamella?, 

 with long or oval lacunae and long branching or bushy canaliculi. The inner 

 one-fifth of the ridge wall is composed of a network of laminae running from 

 the medullary canal to the outer network. The remainder of the bone (anterior, 

 outer, and posterior wall) is composed of a very irregular, wide internal ring 

 of lamellae surrounding the medullary canal and having an outer wavy border, 

 in some places distinct and in other places fused with an external network of 

 laminae. Many canals cross the lamellae on their way from the medullary canal 

 to the middle of the wall. Within the lamellar ring are several round or ellip- 

 tical bodies composed of lamellae running lengthwise of the cross-section. These 

 bodies are such as would result from a transverse section of solid pillars. In 

 the outer wall of the bone lamellae form the entire thickness. Here and there 

 occur a few incomplete Haversian systems consisting of a central canal and 

 radiating canaliculi. Twofold division. 



Type I-II-in, lb. 



FEMUR OF CYNOMYS LUDOVICIANUS. PRAIRIE DOG. CR. MED. COLL. 



Pl. 9, Fig. 183. Syn. Tab. V 



Antero-posterior diameter of bone, 4.5 mm. ; lateral, 5 mm. 



Antero-posterior diameter of medullary canal, 2.5 mm. ; lateral, 3 mm. 



The medullary canal is empty. Medullary index, 50%. 



Structure.— The section is composed of external circumferential lamella' 

 forming an irregular ring which reaches its greatest width in the inner wall. 

 The lacunae are long and narrow and the canaliculi are long. 



The central ring is composed of incomplete Haversian systems of the (lb) 

 differentiation. Their lamellae are indistinct, their lacunae are oval, and their 

 canaliculi are bushy. 



A very wide ring of internal circumferential lamellae surrounds the medul- 

 lary canal. The ring is widest in the anterior wall. Their lacunae are long and 

 narrow and their canaliculi are long. Numerous canals pass from the medul- 

 lary canal across the lamellae into the interior of the bone. 



Type I-III, lb. 



