116 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL.. 35 



KIGHT FEMLK UK FELIS. DOMESTIC CAT. CR. MED. COLL. 



Pl. 14, Fig. 231. Syx. Tab. VI 



Antero-posterior diameter of bone, 7.5 mm. ; lateral, 9.5 mm. 



Autero-posterior diameter of medullary eaiial, 4 mm. ; lateral, 5.5 mm. 



The medullary canal is full. Medullary index, 45%. 



Structure. — External circumferential lamellae form more than one-half of 

 the thickness of the wall of the bone. A few Haversian systems appear in the 

 middle portion of the lamellar ring. They are well developed and without 

 aiiparent signification. A short distance from the mid-line in the inner wall the 

 lamellar ring divides into a wide outer and a narrow inner part which encloses 

 a crescent shaped area of Haversian systems. About the middle of the inner 

 wall is quite a sharp lateral ridge. The lamellar ring is widest at this point and 

 narrowest in the outer wall. The lacunae are long and narrow and the cana- 

 liculi are thickly set, long, and branching. 



The central ring is composed of well developed, large and small Haversian 

 systems, widest in the inner wall and narrowest in the outer wall. The systems 

 are generally strongly developed, and are round, elliptical, or irregular in cross- 

 section. 



The internal circumferential lamellae are in the form of laminae. Their 

 lacunae are long or oval and their canaliculi are bushy. Numerous canals pass 

 through the laminfe on their way from the medullary canal. Four femora of 

 the domestic cat were examined and in each one there was a different develop- 

 ment, structure, and arrangement of bone units. 



Type I-II-IlI, C. 



LEFT FEMUR OF FELIS CATUS. WILD CAT. CR. MED. COLL. 



Pl. 14, Pig. 233. Syx. Tab. VI 



Antero-posterior diameter of bone, 13.5 mm. ; lateral, 11 mm. 



Antero-posterior diameter of the meduUarj^ canal, 8 mm. ; lateral, 5.5 mm. 



The medullary canal is full. Medullary index, 42%. 



Structure.— Arownd the outside of the bone is a ring of lamellae, inter- 

 rupted very frequently by incomplete Haversian systems of the (lb) differ- 

 entiation. The ring forms a greater part of the thickness of the wall of the 

 bone excepting in the posterior wall, where the Haversian systems occupy the 

 whole width from the internal circumferential lamellae outward to the circum- 

 ference. Many canals traverse the ring. For the most part, all of the struc- 

 tural units are rather indistinct. Around the anterior and a portion of the 

 inner wall is a narrow rim of external lamellae. The lacunae of the lamellar 

 ring are long or oval and their canaliculi are long find branching or bushy. 



