THE CIRCULATION OF THE BONE-MARROW. 



35 



In figure 6, which shows the next stage of a partially complete injection, the 

 gross picture observed in figure 4 is again illustrated in the cleared specimen with 

 the marrow in situ. The central vessels are still visible and smaller branches may 

 be seen coming off at an angle from the main artery and extending toward the cir- 

 cumference. These begin almost at the center of the shaft but become more numer- 

 ous and dense toward the ends. At each epiphysis there is a veritable spray-like 

 shower of fine vessels which ramify to every part of the marrow and supply the 

 epiphysis as well, but which stop abruptly at the line of cartilage forming the 

 articulation of the joint (fig. 1). The characteristic vessels of embryonic cartilage 

 have disappeared in the mature state. 



- - 



i 



if Jfc^ . v 



. 



Fig. 1. A detail drawing of a part of the epiphysial end of specimen shown in figure 4 (plate 1). There is a most extensive 

 ramification of the vessels at the epiphysis, radiation stopping abruptly, however, at the line of cartilage. 

 X 140. 



The artery and its branches were easily distinguished from the veins by 

 virtue of their smaller caliber, firmer walls, and less tortuous course; also by the 

 fact that the lumen was more closely packed with particles of carbon. The divisions 

 of the artery were characteristic, the branches came off at an acute angle, and the 

 subdivisions were much less numerous than those of the corresponding veins. 

 The arterioles at the periphery were characteristic in their delicacy, scarcity, 

 and apparently limited distribution. 



Figure 6 illustrates very graphically the "tuft-like" character of the venous 

 branchings. Coming off from the central vessel, almost at right angles, are the 

 large distended veins which at once branch outward toward the circumference 

 in an ever-widening balloon-shaped bed, to anastomose eventually with branches 

 from tufts on either side. The large caliber of the vessels is strikingly maintained; 

 and though there is some decrease in the lumen toward the periphery, it is not 

 commensurate with the extent of the branching. The most apparent and striking 

 thing about the entire vascular system of the bone-marrow, both in gross and in 

 microscopic view, is this extensive venous ramification and its very evident capacity 

 for large quantities of blood. 



A still better comprehension of these venous and arterial tufts and the means 

 by which they become continuous with each other is obtained from a study of a 



