188 



DR. W. N. F. WOODLAND ON THE 



designed for text-fig. 55. In this the axtery and the vein 

 giving rise to a rete mirabile are distinguished from each other 

 by the latter being cross-striped, the subdivision of each of 

 them is indicated, also the intermingling of the fine parallel 

 capillaries, their reunion and the second breaking up into capil- 

 laries of the large arteries and veins thras formed to supply the 

 epithelium of the gas gland. 



Up to the present I have spoken of the arterial and venous 

 capillaries or vessels composing each of the two retia mirabilia 

 merely as tubes, but if, of course, we take into account the 

 direction of the flow of blood in the two sets of vessels, then 

 it is evidently incorrect to speak of the ai-teries and veins both 

 subdividing at the anterior pole of the rete mirabile to prodwce 



Test-fiff. 55, 



Cr.E. 



The constrmction of tile rete mirabile bipolare geminum (R.M.). 

 G.E., glandulai epithelium of gas gland. 



capillaries : what is really happening in this region is that the 

 ?<rteries are subdividing and the veins uniting (text fig. 55). 

 That this is the actual mode of construction of the rete mil a bile 

 is not only proved by the study of serial sections but also by the 

 injection method. And here let me I'emark upon the extra- 

 ordinary process implied by this consti'uction of the rete 

 mirabile — a term which, like its German rendering, "wvmder- 

 netze," happens to be peculiarly appropriate*. It is implied 

 that parallel vessels carrying blood in opposite directions can so 

 influence each other, or be so influenced by a common cause, as 

 to break up into a rete mirabile at the same spot, the subdivision 

 of each of the two sets of vessels being so adapted to the other 

 as to ensure the close apposition and intimate intermingling 

 of their finest capillaries f. It is evident that this intricate 



* Miiller (53) termed tins type of rete mii-ahile a " rete mirahile bipolare gemiimm," 

 in contradistinction to a " rete mirabile bipolare simplex," such as the purely arterial 

 carotid srland of Amphibia. 



t The fact illustrated bj' these retia that blood-vessels are able to capillarize on 

 their own account, i. e. quite apart from any other tissue, first attracted my attention 

 to these " red bodies " when engnsred in certain speculations concerning the "renal- 

 jiortal system " in Vertebrates (76, 77). The formation of the retia seems to lend 

 support to Dr. Shore's views (68, 69) concerning the vascularization of the liver 

 as distinguished from the venous penetration of the kidney-substance to form the 

 "renal-portal system." I hope shortly to investigate the subjects of the"renail- 

 ■portal system'' and the various kinds of retia mirabilia from a practical standpoint. 



