48 



SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE 



VOL. 35 



Structure. — The section is composed of two parts, viz. : A wide ring of 

 external lamellae with oval lacuna? and bushy canaliculi, and a narrow ring of 

 internal lamellae with long, narrow lacunae and straight canaliculi around the 

 medullary canal. Twofold division. 



Type I. 



VII. EEPTILES 



Thirty-four femora were examined. 



General Character oe the Femur 



The general shape of the 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 which are filled with marrow. 



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

 femora. 



The medullary index varies from 0 to 88% with an average 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 bone predominates in both 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 lamellae, and central ring 

 appear, while in the reptiles these divisions are not prominent. Cancellous 

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

 the lizards, and is a characteristic structure of turtles. 



Detailed Examination 



right femur of sphenodon punctata (most primitive of reptiles). 



amer. mus. nat. hist. 



Pl. 3, Fig. 40. Syn. Tais. II 



Antero-posterior diameter of bone, 3 mm. ; lateral, 2.5 mm. 

 Antero-posterior diameter of medullary canal, 1.5 mm.; lateral, 1 mm. 

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



Structure. — The section is composed entirely of concentric lamella; with 

 oval lacunae and bushy canaliculi surrounding the medullary canal. A large 



