34 THE CIRCULATION OF THE BONE-MARROW. 



solution, and then counterstaining for 2 to 3 minutes in a 5 per cent aqueous eosin, 

 gave a beautiful contrast to the cellular elements. Dr. Sabin found that the addi- 

 tion of orange G to the eosin increased the effectiveness of this combination in the 

 staining of embryonic blood-cells. 



OBSERVATIONS. 



In the earlier incomplete injections the gross architecture of the bone-marrow 

 was plainly evident in the cleared specimens. Figure 4 (plate 1) shows the medul- 

 lary artery entering the marrow cavity near the center of the diaphasis, perforating 

 the compact tissue obliquely. It divides immediately into two main branches 

 which diverge abruptly, one extending toward each epiphysis. These two main 

 arterial trunks in turn divide about a third of the way to the epiphyses and extend 

 from their point of origin to the limits of the marrow at either end, anastomosing 

 with the vessels entering there. Several small arteries were usually seen at the epiphy- 

 ses, entering the marrow cavity through the bone, anastomosing with the medul- 

 lary vessels, and helping to furnish the additional blood-supply to the actively 

 functioning red marrow of these regions. 



In addition to this main arterial supply there could be seen numerous small 

 vessels entering along the shaft of the bone (fig. 6), primarily to nourish the cancel- 

 lous and compact tissue, but anastomosing at the periphery with the arterioles 

 of the central vessels. There was frequent and intimate intercommunication along 

 the entire shaft between the nutrient vessels of the Haversian canals and the cir- 

 cumferential end arterioles and venules of the medulla of the bone. These anas- 

 tomoses formed a very striking picture in cleared specimens and gave a new insight 

 into the delicacy of the vascular interfacings and the extent of their ramifications. 

 We are not dealing with two more or less separate and distinct systems, one to 

 nourish the marrow, the other the cancellous and compact tissues, but with one 

 interdependent and communicating whole. The subject of the vascular supply 

 of the bone-substance itself has been treated in a recent monograph by Foote (1921) 

 in a most admirable manner, with extensive illustrations. 



There were three groups of veins in the long bone. (1) The central medullary 

 veins could be seen accompanying the central artery (fig. 4). From one to four 

 parallel veins accompanied the artery and traversed the shaft from each end to unite 

 near the center in a single efferent vein which occupied the nutrient foramen, 

 together with the entering artery. (2) Several large veins emerged near the vas- 

 cular area of red marrow, always more prominent toward the epiphyses. (3) There 

 were numerous small veins along the diaphysis (fig. 6) which drained the compact 

 tissue and the peripheral area of the marrow and, with the small nutrient arterioles 

 of the shaft, formed the abundant vascular network of the periosteum (not shown 

 in the diagram). This general vascular pattern held for both the radius and the 

 ulna of the pigeon, the individual bones differing only in the number of their central 

 vessels, in direct relation to their relative size, and in the extent of bone-marrow 

 to be supplied. In relatively complete injections, the central vessels could not be 

 seen from the surface, even in the most perfectly cleared specimens, so dense was the 

 network of carbon-filled vessels, as will be shown later. 



