126 



SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE 



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. 

 Anteroposterior diameter of medullary canal, 23 mm.; lateral, 21 mm. 

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



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

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

 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. 



External or first ring: This ring is composed of concentric laminae divided 

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

 In the anterior wall the lamina 1 are transformed into irregular Haversian sys- 

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

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

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

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

 aberrant Haversian systems. 



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

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

 short and long laminae 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 laminae of this ring are folded around canalicular 

 expansions into elliptical or elongated angular Haversian systems. As they 

 approach the third ring they are more circular. Their lacunae and canaliculi 

 are like those of the outer ring. 



Internal or third ring: This is composed of vertical and concentric laminae 

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

 posterior wall, and it is here that they are best developed. The laminae of this 

 ring run in various directions and form complex arrangements of structural 

 units. The anterior wall of the bone is composed of irregularly shaped, large, 

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

 is an irregular ring of internal circumferential lamellae having long, narrow 

 lacunae with branching canaliculi. 



Type II-III, C. 



