NO. 3 COMPARATIVE HISTOLOGY OF FEMUR FOOTE 179 



of these spaces aiul lamelke present outlines of crude Haversian systems. The 

 lacunae are round and oval and the canaliculi are sliort and bushy. Beginning 

 on one side of the posterior ridge and extending around the external surface 

 of the bone to the opposite side are a few rather coarse laminse with undulating 

 borders, frequently interrupted by small Haversian systems formed by bending 

 lamellae of the laminfE around the central canals. The systems are elliptical. 

 Under the external laminfe the bone is composed of channelled bone substance, 

 with large meshes visible to the naked eye and having a concentric horseshoe 

 arrangement. Underneath this is a narrow concentric lamina with long lacunae, 

 and under this again is a wide ring of channelled bone substance resembling 

 the external one, but rather more advanced. Around the medullary canal is a 

 very narrow ring of lamella:'. The arrangement of the several rings of thin bone 

 correspond to the groups of vessels and inter-vascular structures seen in figure 

 363, and appears to be a more complete formation. 

 Type I-II-III, la, lb. 



EIGHT FEMUR OF AN EGYPTIAN. NO. 25647!) (a3), U. S. NAT. MUS. 



Pl. 37, Fig. 365. Syn. Tab. IX 



Anteroposterior diameter of bone, 12 mm. ; lateral, 12.5 mm. 



Antero-posterior diameter of medullary canal, 5.5 mm. ; lateral, 7 mm. 



The medullary canal is full. Medullary index, 35%. 



This femur belongs to the same series and shows a further advancement, 

 since the cancellous structure lias disappeared and a compact bone has taken 

 its place. 



Structure. — The [)osterior ridge is composed of Havei-sian systems and 

 vascular canals. Tlieir lacunae are narrow and tlieir canaliculi are long. 



Beginning on one side of the posterior ridge and extending around the 

 section to the other side is a horseshoe band of lamella? of varying widths. It 

 is widest in the posterior wall and remains of uniform width in other situations. 

 The lamellae are interrupted by Haversian systeins of tlie (la) differentiation. 

 Underneath the lamellar band is the middle ring of Haversian systems and 

 inter-Haversian lamellfP. Around the medullary canal is a wide band of lamellae 

 with long lacuna; and straight canaliculi. This bone is more lamellar than Ha- 

 versian system, but it shows a much more advanced stage of formation than 

 those preceding. The completed units have appeared. 



Type I-III, la, C. 



FEMUR OF AN EGYPTIAN. NO. 258675(a), U. S. NAT. MUS. 



Pl. 37, Pig. 366. Syn. Tab. IX 



Antero-posterior diameter of bone, 18 mm. ; lateral, 16.5 mm. 

 Antero-posterior diameter of medullary canal, 10 mm.; lateral, 9 mm. 



