154 



SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE 



vol. 35 



The central ring, forming nearly the whole thickness of the wall of the bone, 

 is composed of well developed Haversian systems with little or no inter-Ha- 

 versian lamella?. The horseshoe areas have been displaced entirely by well 

 developed Haversian systems. The internal circumferential lamellae with long 

 lacuna? and straight canaliculi surround the medullary canal. 

 Type III, C. 



The degree of development of a human femur is proportionate to the degree 

 of displacement of its lamella? or lamina? by Haversian systems. 



FEMUR OF WHITE AND NEGRO MIXED, AT LEAST ONE-HALF WHITE. 



no. 247368, u. s. nat. mus. 

 Pl. 21, Fig. 307. Syn. Tab. VIII 



Antero-posterior diameter of bone, 22 mm. ; lateral, 27 mm. 



Antero-posterior diameter of medullary canal, 12 mm.; lateral, 11 mm. 



The medullary canal is full. Medullary index, 30%. 

 Structure. — The external circumferential lamella?, in fragments, surround the 

 bone. Their lacuna? and canaliculi are well developed. There is little evidence 

 of the horseshoe band of lamella?. The central ring is composed of Haversian 

 systems and forms nearly the whole width of the wall. The systems are of 

 unequal sizes, some are small and others are large relatively, but generally they 

 are rather small. There is also a corresponding variation in the diameters 

 of the Haversian canals. The lacuna? and canaliculi of the Haversian systems 

 are of the fully developed variety. Many Haversian systems are senile. 



The internal circumferential lamella? with long lacuna? and straight cana- 

 liculi surround the medullary canal. 



Type III, C, senile. 



LEFT FEMUR OF A NEGRO. NO. 3, MED. DEPT. TULANE UNIV. 



Pl. 21, Fig. 308. Syn. Tab. VIII 



Antero-posterior diameter of bone, 30 mm. ; lateral, 24 mm. 

 Antero-posterior diameter of medullary canal, 15 mm. ; lateral, 14 mm. 

 The medullary canal is full. Medullary index, 41%. 



Structure. — External circumferential lamella? with long lacuna? and straight 

 canaliculi are fragmentary. The central ring forms most of the bone and is 

 composed of Haversian systems of the (C) differentiation. Many show senile 

 changes. A narrow ring of internal circumferential lamella? surrounds the 

 medullary canal. 



Type III, C, senile. 



