146 SMITHSONIAX COITTRIBrTIOXS TO KNOWLEDGE VOL. 35 



RIGHT FEMUE OF MELURSUS LABL^TUS. SLOTH BEAK. XU. 22720, 

 AMEE. MUS. XAT. HIST. 



Pl. 20, Fig. 293. Stn. Tab. VII 



Antero-posterior diameter of boue, 24 mm. ; lateral, 24 mm. 



Antero-posterior diameter of medullary canal, 10 mm.; lateral, 10 mm. 



The medullary canal is full. Medullary index, 21%. 



Structure. — A horseshoe band of lamellfe, lamina^, and Haversian systems 

 of the (la) differentiation embraces the posterior ridge. The band is widest 

 in the inner wall, where it is composed of lamellse and lamina} alternating with 

 Haversian systems. The lacunae are oval and long. 



The central ring is composed of lamellae, laminae, and Haversian systems 

 intermixed and alternating with each other. The systems are well developed. 

 The posterior ridge is composed of Haversian systems and lamellas having a 

 direction from the external to the medullary surface. 



The internal circumferential lamellae form a narrow ring around the medul- 

 lar}^ canal. The lacunae are long. 



The bone is peculiar in the mixture of its units. 



Type I-II-III, la, C. 



LEFT FEMUR OF CANIS AURET'S. JACKAL. XO. 163293, U. S. NAT MUS. 



Pl. 30. Fig. 294. Syx. Tab. VII 



Antero-posterior diameter of bone, 10 nnn. ; lateral, 8.5 mm. 



Antero-posterior diameter of medullary canal, 6.5 mm. : lateral. 6 mm. 



The medullary canal is full. Medullary index, 85%. 



Structure.- — An irregular horseshoe of lamellae and lamiiut surrounds the 

 section. On the outer side of the posterior ridge the lamellae are wide, as they 

 extend around the outer lateral wall they become very narrow, then widen 

 again in the anterior wall to more than lialf tlie width, and as they pass around 

 the inner wall they separate into lamina, diminish in width, and terminate in the 

 iimer posterior region. The lamelhp are interrupted by Haversian systems of 

 the (la) ditferentiation. They are frequently crossed by canals. Underneath 

 the lamella? and laminse is an irregularly shaped central ring of Haversian sys- 

 tems. It forms the whole width of the posterior and adjacent inner wall. The 

 systems are large and small and well developed. In the outer wall thej^ are 

 elongated in cross-section, especially in the anterior region. A narrow ring of 

 internal circumferential lamellse surrounds tlie medullary canal. 



Type I-II-III, la, C. 



