HUMAN TESTIS AND EPIDIDYMIS 401 



glomeruli of the mesonephros, the other from the sinusoids. Both 

 sets interdigitate with the network of cords, and extend beyond the 

 the outer cross connections of the network so as to lie just under- 

 neath the peritoneal epithelium. The flow of blood is in two 

 directions from the hilus or mediastinum testis toward the peri- 

 phery, and from the periphery toward the center; the veins also 

 return the blood in both directions. There are at first, then, no 

 terminal arteries or veins. As certain cords become destroyed, 

 the capillaries lying near them are allowed to assume a straighter 

 course; they then become the more favored vessels, grow larger 

 and are established as main arteries or veins. Since the cross 

 connections of the network are those most frequently severed, 

 the radial vessels are the most favored, and hence the main arteries 

 and veins of the testis run radially. But not infrequently, as we 

 have seen, the radial cords are severed, and this fact accounts 

 for the few main vessels which, though not figured by Hill, are 

 commonly present in the adult testis, running diagonally or even 

 for some distance parallel to the surface of the gland, quite deep 

 within the substance. Another curious arrangement of vessels 

 not mentioned by Hill, is found in the testis ; three or four arteries 

 run parallel to one another for long distances to supply an area 

 which would usually be served by a single artery with short 

 branches. To explain this it is only necessary to imagine that 

 certain cross connections of the cord network which may at first 

 have separated the different vessels quite widely, were destroyed 

 late, after each vessel was well established, and that subsequent 

 radial growth drew the vessels together. 



The terminal arteries are at their first appearance probably 

 portions of the capillary network not favored by a direct course. 

 In the fourth month three sets of terminal arteries can be made out, 

 one set situated between the outer and second sets of cross con- 

 nections of the testis cords, another between the second and inner 

 sets of cross connections, and a third set nearer the rete. At seven 

 months new arteries have grown from these, and also apparently 

 from the main stems of the radial and peripheral arteries, so that 

 the picture is much complicated; yet even in the adult, the embry- 

 onic arrangement of three main branches from each radial artery 



