NO. 3 COMPARATIVE HISTOLOGY OF FEMUR FOOTE 153 



RIGHT FEMUR OF CRANIORRHACHISCHISIS WHITE FETUS. NO. 91, CR. MED. COLL. 



Pl. 31, Fig. 305. Syn. Tab. VIII 



Antero-posterior diameter of bone, 6 mm. ; lateral, 6 mm. 



Antero-posterior diameter of medullary caual, 3 mm.; lateral, 2.5 mm. 



The medullary canal is full. Medullary index, 267c- 



Structure. — The bone has no distinct divisions. The anterior wall is thin- 

 nest; the posterior is thickest. The bone is composed of a wide horseshoe of 

 irregular, concentric lamiiife with wide canals surrounding the medullary canal. 

 The laminae of the posterior ridge witli their wide canals shorten, widen, and 

 become crude, elongated Haversian systems, running from the external to the 

 medullary surface and at right angles to the lamina? of the lateral wall. The 

 lacunae are oval and the canaliculi are bushy. The femur is larger than that 

 of the normal fetus of the same age. 



Type II-III, lb. 



In the development of human fetal femora some of the Haversian systems 

 appear to be produced by tlie aberrant method of formation; that is, by the 

 transformation of laminae into Haversian systems. 



XII. MAN— BLACK EACE 



General Character of the Femur 



The bones vary in shape. The medullary canals are full and cancellous 

 bone is prominent. The medullary surfaces are very much corrugated and 

 irregular in character. The medullary index varies from 17% to 92%, with 

 an average of 41.9 %o. The type of structure ranges from a first and third to a 

 complete third, and the majority are type combinations rather than single types. 

 The first and third and first, second and third are the most frequent combina- 

 tions. Senile changes are found in many femora. The bone units are incom- 

 pletely and completely differentiated. 



Detailed Examination 



left femur of negro. no. 228481, u. s. nat. mus. 



Pl. 21, Fig. 306. Stn. Tab. VIII 



Antero-posterior diameter of bone, 29 mm. ; lateral, 30 mm. 

 Antero-posterior diameter of medullary canal, 16 mm. ; lateral, 15 mm. 

 ' The medullary canal is full. Medullary index, 38%c. 

 Structure.— The external circumferential lamellae, in fragments, surround 

 the bone. The lacuna? are long and narrow and the canaliculi are straight. 



