152 



SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE 



vol. 35 



where the wall of the bone has united or is about to unite. Many large oval 

 lacunas are found in the bone substance between the systems. The bone shows 

 the formation of Haversian systems, the filling of the posterior ridge by laminae 

 at right angles to the lateral walls, and the line of union as the walls fuse 

 together in the posterior ridge. A wide band of lamellae with oval lacunae and 

 bushy canaliculi surrounds the medullary canal. 

 Type II-III, lb. 



EIGHT FEMUR OF AMERICAN NEGRO FETUS, NINE MONTHS. NO. 228801, 



U. S. NAT. MUS. 



Pl. 21, Fig. 304. Syn. Tab. VIII 



Antero-posterior diameter of bone, 4.5 mm.; lateral, 5.5 mm. 

 Antero-posterior diameter of medullary canal, 1.5 mm. ; lateral, 2.5 mm. 

 The medullary canal is full. Medullary index, 15%. 



Structure. — The anterior wall is composed of a few external circumferen- 

 tial lamellae, which, as they leave the mid-line, soon spread out and enclose 

 elongated, crude Haversian systems of the (lb) differentiation. The systems, 

 which appear to be laminae crudely bent around and along wide, short canals, 

 assume a concentric arrangement and enclose the medullary canal in the form 

 of a horseshoe. The posterior ridge is then formed and fuses with the lateral 

 wall. The lacunae are oval; the canaliculi are comparatively few and bushy. 

 In the mid-line of the anterior wall the external circumferential lamellae are 

 distinctly separated from the crude Haversian systems, but this line of separa- 

 tion soon becomes indistinct. The Haversian systems vary in shape and com- 

 pleteness in the different portions of the wall. In the anterior portion they 

 are round or oval, especially just beneath the external circumferential lamellae 

 where they are most complete. The Haversian canals are relatively wide. The 

 lacunae of the systems form single concentric rings around the Haversian 

 canals and at some distance from them. They are oval with short, bushy cana- 

 liculi. The Haversian systems gradually elongate and become extremely ellip- 

 tical as they approach the posterior ridge. Here the Haversian canals are 

 long, wide, and generally parallel. They occupy nearly the whole thickness of 

 the posterior wall and extend from the external to the medullary surface. The 

 Haversian canals of the lateral wall are wide, irregular, and long, but are 

 generally parallel with the external surface of the bone. The lacunae are oval, 

 few, and confined to a single concentric row situated at some distance from the 

 canal. The posterior ridge appears to be formed at a later date than the 

 anterior and lateral walls. The internal circumferential lamellae with long 

 lacunae and straight canaliculi are present in the anterior wall, but not else- 

 where. 



Type II-III, lb. 



