^O. 3 COMPARATIVE HISTOLOGY OF FEMIT]^ FOOTE 113 



Stn(cture.--Beghmmg on both sides of the posterior ridge and extending 

 around the external aspect of the bone is a wide horseshoe-shaped band of 

 lamellas with long and oval lacunae and straight and bushy canalieuli. The la- 

 mellae are interrupted by crude Haversian systems of the (la) differentiation 

 and crossed at various angles by numerous canals. 



The central ring is composed of well developed Haversian systems and 

 inter-Haversian lamelte. Their lacunae are long and canalieuli are straight. 

 The ring is narrow in the anterior wall and widens as it encircles the lateral 

 and posterior wall. In the posterior ridge the systems form the whole thickness 

 of the wall and are embraced by the heel of the horseshoe band. The internal 

 circumferential lamellae form a narrow ring around the medullary canal. 



More than half of the section is lamellar. In this respect it differs from 

 the orang-utan in the femur of which the external lamellas form a narrower ring. 



Type I-III, la, C. 



FEMUR OF PRESBYTIS EUBICtlNDA. MOSTKEY. NO. 153793, U. S. NAT. MI'S. 



Pl. 13, Fig. 226. Syn. Tab. VI 



Antero-posterior diameter of bone, 11 mm. ; lateral, 11 mm. 



Antero-posterior diameter of medullary canal, 6 mm. ; lateral, 6.5 mm. 



The medullary canal is full. Medullary index, 48%. 



Structure. — A wide irreg-ularly shaped horseshoe of lamelte surrounds the 

 section. The lamellae form about one-half of the thickness of the inner and 

 anterior wall and practically the whole thickness of the outer wall. They are 

 well developed with narrow lacunae and long canalieuli and are frequently inter- 

 I'upted by Haversian canals of the (la) differentiation. 



The central ring is interrupted by the external lamellae of the outer wall. 

 It is narrow and composed of fairly well developed Haversian systems with 

 considerable inter-lamellar structure. The posterior ridge is composed of la- 

 mellae and Haversian systems mixed. The systems have oval and narrow lacunte 

 and rather infrequent canalieuli. The internal circumferential lamelte form a 

 narrow ring around the medullary canal. 



Type I-TII, la, C. 



EIGHT FEMUR OF HYLOBATES. GIBBON. NO. 131988, U. S. NAT. MUS. 



Pl. 13, Fig. 227. Syn. Tab. VI 



Antero-posterior diameter of bone, 11 mm.; lateral, 11.5 mm. 



Antero-posterior diameter of medullary canal, 6 mm. ; lateral, 6.5 mm. 



The medullary canal is full. Medullaiy index, 44%. 



Structure. — The section of the bone is composed of a wide external ring of 

 lamella?, frequently interrupted by very incomplete Haversian systems of the 

 (la) differentiation. The lamellar ring surrounds the bone with the exception 



