NO. 3 COMPARATIVE HISTOLOGY OF FEMUR FOOTE 37 



and most complete. They are all of the first type, though of different develop- 

 ments. In figure 1 the radiating canals with poorly developed intervening 

 lamella? indicate an early stage of development. In figure 2 more than half of 

 the canals have disappeared and hetter developed lamella; are formed. In 

 figure 3 all of the canals ha\-e disappeared and the whole bone is composed of 

 concentric lamellte. 

 Type I. 



EIGHT FEMUR OF RANA CATESBIANA (SMALL). FOURTH BULL FROG. CH. MEL). COLIi. 



Pl. 1, Fig. 4. Syn. Tab. I 



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



Antero-posterior diameter of medullary canal, 0.5 mm.; lateral, 0.6 mm. 



Medullary index, 24%. 



Structure. — The section is composed of concentric lamellfe with long lacunas 

 and long, straight eanaliculi surrounding the medullary canal. The section has 

 a uniform structure. 



Type I. 



fractured and rep.\ikeu femur of a frog. cr. med. coll. 

 Pl. 1, Fig. 5. Syn. Tab. 1 



Antero-posterior diameter of bone, 1.5 nun.; lateral, 1.7 nnn. 



Antero-posterior diameter of medullary canal, 0.6 mm.; lateral, 0.7 nniL 



The medullary canal is full. Medullary index, 20%. 



Structure. — One of the femora had lieen fractured about tlie middle of tlie 

 shaft. The ends of the bone liad slipped by each otlier, and new bone had 

 formed around the fragments. In section (fig. 5) which was taken from tlie 

 middle of the new bone, two cuts of the femur appear situated eccentrically. 

 The sections are composed of concentric lamella^ with oval and straight lacuna- 

 surrounding the medullary canals. 



The upper fragment, H, proximal, shows cell growtlis bursting through the 

 wall of the bone (pl. 1, fig. 5, A, B). In the lower fragment, D, distal, no cell 

 outbursts appear. 



Around the two fragments and extending between them is a formation of 

 cancellous or channeled bone which is the new bone of repair. Some of the 

 meshes of this bone are occupied by newly deposited lamelhe, and resemble 

 Haversian systems, altJiough there are no Haversian systems or cancellous 

 bone in the femur of tbc frog (i)l. 1, fig. 5 (',.R). This fact suggests a genetic 

 relationship between cancellous lione and Haversian systems. 



Type I. 



