160 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 35 



Structure. — Beginning on both sides of the posterior ridge and extending 

 around the section is a horseshoe of lamellfe, lamiuaB, and Haversian systems 

 of the (la) and (C) differentiations. The shoe is crossed by frequent canals. 

 Under the horseshoe is a middle ring of well developed Haversian systems which 

 reaches the external surface of the posterior ridge. 



Internal circumferential lamellae form a narrow ring around the medullary 

 canal. The section is nearly half lamelliB. 



Type I-II-III, la, C. 



BIGHT FEMUR OF A KAFFIR NEGRO. NO. 263196, U. S. NAT. MUS. 



Pl. 23, Fig. 324. Syn. Tab. VIII 



Antero-posterior diameter of bone, 27 mm. ; lateral, 23 mm. 



Antero-posterior diameter of medullary canal, 14 mm. ; lateral, 11.5 mm. 



The medullary canal is partly surrounded by cancellous bone and is full. 

 Medullary index, 32%. 



Structure. — The external circumferential lamelte are fragmentary. Be- 

 ginning on the outer side of the posterior ridge and extending around the outer 

 lateral wall is a wide external band of elongated Haversian systems in a back- 

 ground of lamella;. This band, one-half the width of the wall, bends inward 

 toward the internal circumferential lamellae as it approaches the anterior wall 

 and then merges into the Haversian systems of that wall. In the inner wall is 

 a similar, narrower external band beginning near the posterior ridge, extending 

 around the lateral, widening, curving inward toward the medullary canal, and 

 merging into the Haversian systems of the anterior wall. These bands are the 

 remains of the lamellar horseshoe. Their lacunas are oval and narrow. Under- 

 neath these bands is an irregularly shaped ring of well developed Haversian 

 systems forming nearly the whole width of the anterior and posterior wall. 

 They communicate freely by cross canals and their lacunae are well developed. 

 The internal circumferential lamellae surround the medullary canal as cancellous 

 bone. In the lateral inner wall they widen and separate into lamina^, which 

 spread toward the external surface and occupy half of the width of the wall in 

 the widest place. The lacunae are oval and narrow. 



Type I-III, C. 



right femur of A NEGRO. NO. 248674, U. S. NAT. MUS. 



Pl. 23, Fig. 325. Syn. Tab. VIII 



Antero-posterior diameter of bone, 30 mm.; lateral, 26 nun. 

 Antero-posterior diameter of medullary canal, 15 mm.; lateral, 12.5 mm. 

 There is little cancellous bone around the medullary canal. Tlie bone is a 

 little larger than the left femur. 



The medullary canal is full. Medullary index, 32%. 



