48 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 35 



Structure. — The seftioii is comijosed of two parts, viz. : A wide riug of 

 external lamellae with o\al lacunae and bnsliy canalicnli, and a narrow ring of 

 internal lamelte with long, narrow lacunae and straight canalicnli around the 

 medullar}' canal. Twofold division. 



Type I. 



VII. REPTILES 



Thirty-four femora were examined. 



General Character of the Femur 



The general shape of tJie reptilian femur varies considerably. The tri- 

 angular, elliptical, round, and indeterminate forms are present. The majority 

 are elliptical. In some sections the antero-posterior diameters are longest, as 

 in many of the lizards, and in others the lateral diameters are longest, as in 

 the turtles. 



The contents of the medullary canals are variable in character. In the 

 lizards they are filled with marrow and in the turtle with cancellous bone, the 

 meshes of wliich are filled with marrow. 



The medullary surfaces are smooth in tlie small, and rough in the large, 

 femora. 



The medullary index varies from to 88% with an a\erage of 26.1%. 

 Excluding the turtles, in most of which the index is zero, the average is 33%. 



The reptilian femora follow about the same kind of development as was 

 seen in the amphibians, but the development is carried further. 



The first type of Ixme predominates in liotli amphibians and reptiles. Ha- 

 versian canals, (la) stage, appear in the amphibians, while a better developed 

 form of Haversian system, (lb) stage, is found in some of the reptiles. In the 

 amphibians the external, internal circumferential lamella', and central ring 

 ai)i)ear, while in the reptiles these divisions are not prominent. Cancellous 

 bone was found in (iiie amphibian, the Amblystoma. It does not appear in 

 the lizards, and is a characteristic structure of turtles. 



Det.ailed Examination 



RiriTIT FEMUR OF SPHENODON PUNCTATA (mOST PRIMITIVE OF REPTILES). 



AMER. MUS. NAT. HLST. 



Pl. 3, Fig. 40. Syn. Tah. 1 1 



Antero-]Kistei-i()r diameter of bone, .'! nun.; lateral, 2.") mm. 

 Antero-])osterioi' diameter of medullary canal, 1.3 nun.; lateral, 1 mm. 

 The medullary canal is full. Medullary index, 26%. 



Stnicturc. — The section is composed entirely of concentric lamella' with 

 oval lacuna' and busliv i-anaiiculi surrounding ihe nicihillary canal. A large 



