NO. 3 



COMPARATIVE HISTOLOGY OF FEMUR FOOTB 



59 



Structure. — The section is composed of lamellae with oval lacuna? and bushy 

 canaliculi, incompletely separated into laminae which surround the medullary 

 canal. In the posterior wall the crude laminae are frequently interrupted by 

 Haversian canals of the (lb) differentiation. In the internal laminae of the 

 anterior wall are several crude undeveloped and a few fairly well developed 

 Haversian systems. The medullary canal is occupied by cancellous bone. 



Type I-II-III, lb. 



RIGHT FEMUR OF TESTUDO (GOPHERUS) POLYPHEMUS. NO. 7555, U. S. NAT. MUS. 



Pl. 4, Fig. 73. Syn. Tab. II 



Antero-posterior diameter of bone, 8.5 mm. ; lateral, 6 mm. 



Antero-posterior diameter of medullary canal — cancellous bone. 



The medullary canal is full. Medullary index, 0. 

 . Structure.- — The section is composed of incompletely formed, concentric 

 laminae which constitute the anterior, outer, and posterior wall. The laminae 

 are crossed by short, radiating canals and interrupted by Haversian systems 

 of the (la) differentiation. Beneath the laminae of the anterior and outer 

 wall are Haversian systems of the (lb) stage of development and the posterior 

 ridge is made up almost entirely of Haversian systems of the same develop- 

 ment. The inner wall is composed of lamellae. 



Type I-III, la, lb. 



VIII. BIRDS 



Forty femora were examined. 



General Character of the Femur 



The femora of birds vary considerably in shape. A few are triangular, 

 many are elliptical, and some are circular. The majority of them are elliptical 

 and their antero-posterior diameters are longest. The medullary contents pre- 

 sent a variable character. In some femora the medullary canals are full of 

 marrow; in some, of cancellous bone, the meshes of which are filled with mar- 

 row; while in others, the canals are empty or occupied by trabeculae only. About 

 half of the femora examined have no contents. 



The medullary surfaces also vary somewhat in character. In those canals 

 filled with marrow and blood vessels the surface is uneven, while in those 

 which have no contents the surface is smooth. In these bones the walls are thin, 

 the canals large, and the trabeculae are numerous. The medullary index varies 

 from 0 to 327%, with an average of 159%. 



The bone structures show considerable variation. The three single types 

 and many combinations of types, in an incomplete or complete differentiation, 



