NO. 3 COMPARATIVE HISTOLOGY OF FEMUK FOOTE 161 



Structure. — The external circumferential lamelte are not distinct from the 

 underlying- structures. Beginning- on both sides of tlie posterior ridge and ex- 

 tending around the section is a wide horseshoe-shaped band of lamina and 

 lamellae. The toe of tlie shoe forms nearly the whole of the anterior wall and 

 the heel nearly one-third of the posterior wall. In the outer lateral wall the 

 heel of the shoe is composed of lamina, separated by canals and crude Ha- 

 versian systems. The laminae gradually widen and increase in number and 

 bend inwards nearly to the medullary canal as they reach the anterior wall. 

 Here the laminar structure spreads out into a wide band of lamellae which forms 

 nearly all of the anterior wall. In this band are a great number of crude 

 Haversian systems of the (la) differentiation arranged in concentric lines. 

 After leaving the anterior, tlie lamellae gradually become narrow until they 

 form about one-third the width of the posterior wall. Underneath the horse- 

 shoe band is an irregularly shaped ring of Haversian systems which widens 

 and forms nearly the whole posterior ridge. The systems are often separated 

 by lamellae. The internal circumferential lamellis surround the medullary canal 

 and are widest in the outer wall. The lacunae are oval and narrow. 



Type I-II-III, la, C. 



LEFT FEMUR OF A NEGKO. NO. 248674, U. S. NAT. MUS. 



Pl. 24, Fig. 326. Syn. Tab. VIII 



Antero-posterior diameter of bone, 29 mm. ; lateral, 27 mm. 



Antero-posterior diameter of medullary canal, 17 mm. ; lateral, 14 mm. 



The medullary canal is full. Medullary index, 42%. 



Structure.— Begmnmg on both sides of the posterior ridge and extending 

 around the external portion of tlie section is a wide horseshoe-shaped band of 

 laminae, lamellae, and Haversian systems. In the outer wall the heel is com- 

 posed of a wide band of lamella;, interrupted by a few Haversian systems of 

 the (la) differentiation, and in the inner wall of laminae with many systems of 

 the same grade. The lamellar and laminar bands rapidly widen about the mid- 

 lateral wall and bend inward nearly to the medullary canal as tliey reach the 

 anterior and form the whole width of the anterior wall, excepting- the internal 

 circumferential lamellae. In the anterior wall the lamelliB form a background 

 which is thickly set with crude Haversian systems of the (la) differentiation. 

 Underneath the horseshoe and between it and tlie medullary canal the following 

 structures are found: In the inner wall short, wide, irregular bands appear, 

 interrupted by Haversian systems, well developed. In the outer wall the sys- 

 tems are much more closely set and better developed. The posterior ridge is 

 composed entirely of systems, well developed. The lacunae are well developed. 



