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SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE 



VOL. 35 



of the posterior ridge, where a few Haversian systems reach the external sur- 

 face and blend with a few tendon insertions. 



The central ring is composed of Haversian systems of the (C) differentia- 

 tion which displace the internal circumferential lamellae in the outer lateral wall 

 and border on the medullary canal. Their lacunae and canaliculi are well 

 developed. The internal circumferential lamellae surround the medullary canal 

 excepting a small part of the outer lateral wall. 



Type I-III, la, C. 



LEFT FEMUR OF ANTHROPOPITHECUS TROGLODYTES. CHIMPANZEE. NO. 18010, 



AMER. MUS. NAT. HIST. 



Pl. 13, Fig. 228. Syn. Tab. VI 



Antero-posterior diameter of bone, 13 mm. ; lateral, 16 mm. 

 Antero-posterior diameter of medullary canal, 6 mm.; lateral, 8 mm. 

 The medullary canal is full. Medullary index, 30%. 



Structure. — The external circumferential lamellae surround the section. 

 This lamellar ring is widest in the antero-inner lateral wall where it constitutes 

 nearly the whole thickness of the wall. It is narrowest in the posterior wall. 

 Its lamellae have long lacunae with straight canaliculi. The ring is interrupted 

 by crude Haversian systems of the (la) differentiation and crossed by canals. 



The central ring, irregular in width, is composed of well developed Ha- 

 versian systems. 



The internal circumferential lamellae form a narrow ring around the medul- 

 lary canal. Just external to this ring is a concentric row of vascular spaces. 

 The lacunae are long. 



The bone is, however, more than half lamellae. 



Type I-III, la, C. 



RIGHT FEMUR OF MACACUS RHESUS. INDIAN MONKEY. R. I. 



Pl. 14, Fig. 229. Syn. Tab. VI 



Antero-posterior diameter of bone, 8 mm. ; lateral, 8.5 mm. 

 Antero-posterior diameter of medullary canal, 5 mm.; lateral, 5.5 mm. 

 The medullary canal is full. Medullary index, 68%. 



Structure. — There are no external and internal circumferential lamellae dis- 

 tinct from the central ring of the bone. 



A crescent of well developed Haversian systems, bordering upon the inner 

 wall of the medullary canal, begins in the posterior region and extends around 

 the inner and anterior to the outer wall, where it merges into the lamellar struc- 

 ture. The widest part of the crescent forms about one-third of the entire 

 thickness of the inner wall. 



