126 SMITHSONIAN CONTRIBUTIONS TO KNOWI.EDOE VOL. 35 



LEFT FEMUR OF BOS. DOMESTIC OX. CR. MED. COLL. 



Pl. 16, Fig. 252. Syn. Tab. VI 



Antero-posterior diameter of bone, 44 mm. ; lateral, 39 mm. 



Antero-posterior diameter of medullary canal, 23 mm. ; lateral, 21 mm. 



The medullary canal is full. Medullary index, 4:0%. 



Structure. — The bone is composed of three wide concentric rings with 

 irregular boundaries, separated by canals containing chains of black laeunar- 

 like bodies with connecting and very irregular canalicular extensions. In thin 

 sections there appear to be no uniting structures in the canals of sufficient 

 importance to hold the rings together. 



The canals have an undulating course and communicate with other canals 

 of the rings. 



Extenuil or first ring: This ring is composed of concentric laminje divided 

 into short lengths. Occasionally a few Haversian systems interrupt the lamina. 

 In the anterior wall the lamiufe are transformed into irregular Haversian sys- 

 tems which have their best development in the middle jjortion of tiie walls. The 

 laminae have long or oval lacuna and branching or bushy canaliculi. Some 

 lamina are solid; some have central canals; and some show these canals en- 

 larged at intervals with the lamelhe bending around the enlargements, forming 

 aberrant Haversian systems. 



Middle or second ring: The borders of the separating canals are composed 

 of clear lamella^ with no visible canaliculi. The second ring is composed of 

 shorl and long lamina; arranged vertically to the outer ring, especially in the 

 inner wall. Along the outer border of the separating canal the lamina is con- 

 centric. As it approaches the anterior projecting wall it merges into the 

 irregular Haversian systems of that region. In the outer wall the laminae are 

 much more concentric. The lamina; of this ring are folded around canalicular 

 expansions into elliptical or elongated angular Haversian systems. As they 

 af)proach the third ring they are more circular. Their lacuuix; and canaliculi 

 are like those of tlie outer ring. 



Internal or tlurd ring: This is composed of vertical and concentric lamiuffi 

 of an Haversian system character intermixed. There are more systems in the 

 poslei-ior wall, and it is here that Ihey are Ijest developed. The lamiiUB of this 

 ring run in various dii-ci-tiuiis and foiiu cinnplex arrangements of stnictni-al 

 units. The aiitcrioi- wall ol' the l)one is composed of irregularly shaped, large, 

 crude Haversian systems united by short lainelhe. Around the medullary canal 

 is an irregular ring of internal circmnferential lamella' having long, narrow 

 lacuna} with branching canaliculi. 



Type II-III, C. 



