NO. 10 THE CIRCULATORY SYSTEM IN BONE — FOOTE 5 



LONGITUDINAL SECTION OF THE SAME FEMUR SHOWING THE 

 CIRCULATION 



Pl. I, Fig. 5 



The oblique entering canals in the shafts of the femora of bull 

 frogs, for the passage of the medullary arteries, are found in the bone 

 of the large and medium sized but not in the small animals. As the 

 femur of the frog is small and round the circulation in a tangential 

 section could not be seen. The general plan, however, is shown in a 

 longitudinal section of the inner wall as represented in figure 5, 

 plate I. The letter C is placed at the center of the shaft. In this wall 

 are two sets of six or seven oblique vascular canals entering the shaft 

 from the periosteal surface and united in such a manner as to form 

 slanting m-shaped converging loops. These loops, beginning near 

 the extremities of the shaft, converge toward the lineal center and 

 medullary surface. From these loops and their stems minute can- 

 aliculi are sent ofif into the bone substance where they communicate 

 with the lacunae. Between the two sets of converging loops are short 

 segments of loops extending across the wall transversely. In the 

 outer wall the loops are not seen in longitudinal section nor are the 

 radiating vascular channels seen in the cross section of this wall. 



CROSS AND TANGENTIAL SECTIONS OF THE FEMUR OF THE 

 REPTILE, ALLIGATOR MISSISSIPPIENSIS 



CROSS SECTION SHOWING THE STRUCTURE 



Pl. I, Fig. 6 



This section is composed of three wide, concentric rings of incom- 

 pletely differentiated Haversian systems alternating with two narrow, 

 concentric laminae. The vascular canals surrounded by clear areas 

 similar to those seen in the bone of the fish are early forms of 

 Haversian systems. The laminae are more advanced in differentia- 

 tion than the Haversian systems. The bone, as a whole, shows an 

 early second and third type structure. 



TANGENTIAL SECTION OF THE SAME FEMUR, SHOWING THE 

 CIRCULATION 



Pl. I, Fig. 7 



The circulation is in the form of a vascular plexus. The section 

 is situated below the periosteal surface near the posterior ridge. 

 Several entering canals, without surrounding lamellae, are seen in 



