NO. 3 COMPARATIVE HISTOLOGY OF FEMUR FOOTE 169 



by spaces similar to lliose iiientioned above. Tlie systems are louiul, oval, and 

 irregular in shape with oval lacunas and straight canaliouli. They communicate 

 by cross canals. The posterior ridge is nearly all Haversian systems. 



A ring of internal circumferential lamellae of varying widths surrounds the 

 medullary canal. In the lateral wall it spreads out into a fan-shaped area, 

 which occupies about half the wall and is interrupted ])y a few canals. 



Type I-II-III, la, C. 



FEMUR OF A PUEBLO INDIAN, NO. 258675 (x), U. S. NAT. MUS. 



Pl. 36, Fig. 343. Syn. Tab. IX 



Antero-jjosterior diameter of bone, 20 mm. ; lateral, 20 nmi. 



Antero-posterior diameter of medullary canal, 8 mm.; lateral, !• mm. 



The medullary canal is full. Medullary index, 22%. 



Stnicfiire. — The posterior ridge, not prominent, is composed of Haversian 

 systems which are well developed. Beginning on both sides of tlie ridge 

 and extending completely around the bone is a wide horseshoe of lamellae, sep- 

 arating in places into lamina', which are interrupted by Haversian systems of 

 the (la) differentiation. The horseshoe varies in thickness. Tlie toe constitutes 

 two-thirds the width of the anterior wall, while the heel is considerably nar- 

 rower. In the anterior wall the lamellaj are very frequently interrupted by 

 elongated Haversian systems arranged concentrically. These systems are crude 

 and of a low development. 



Underneatli the lamellar horseshoe is a central ring of complete Haversian 

 systems. They are well developed with long, narrow lacunae and straight cana- 

 liculi. Internal circumferential lamellae enclose the medullary canal. In tlie 

 ])osterior wall they form a wide band. In other situations they are reduced 

 to a narrow ring. 



Type I-II-III, la, C. 



RIGHT FEMUR OK A PITICBLO INDIAN, ADULT. NO. 227339, U. S. NAT. MUS. 



Pi,. 2(1 Fig. 344. Syn. Tab. IX 



Antero-posterior diameter of bone, 25 mm. ; lateral, 2."! nun. 



Antero-posterior diameter of medullary canal, 14 mm.; lateral, 11 mm. 



The medullary canal is full. Medullary index, 37%. 



Structure. — The external circumferential lariiellae appear in scattered frag- 

 ments around the section, and whole or half Haversian systems occupy the 

 intervals between the fragments. The lacunae are oval and long. A thick cen- 

 tral ring of Haversian systems forms the chief part of the wall of the bone. The 

 systems are well developed, their lacunae are long and narrow. Extending 

 across the prominence of the inner wall and forming its external boundary the 

 Haversian systems are somewhat elongated and arranged in a direction parallel 



