88 ALLEN 



sends off, or receives, a cross vessel from the corresponding 

 vein on the opposite side. This cross vessel receives a branch, 

 coming caudad along the dorsal surface of the oblongata. 

 Whether it returns any of the venous blood from the cerebellum 

 I was unable to determine. In the neighborhood of the origin 

 of the vagus portion of the ramus lateralis accessorius from the 

 dorsal root of the vagus, the posterior encephalic vein re- 

 ceives an anterior branch or oblongata vein (PI. Ill, fig. 24 ; 

 Obi. v.), which has its source from the side of the oblongata 

 directly behind the roots of trigemino-facial complex, and 

 shortly receives a branch from the posterior ampulla, then run- 

 ning along the side of the oblongata, passes beneath the IX and 

 X nerves and finally terminates by emptying into the posterior 

 encephalic vein. Following along the dorsal root of the vagus 

 nerve the posterior encephalic vein leaves the brain case 

 through the vagus foramen in the exoccipital, but before leav- 

 ing the skull the large myelonal vein is received from the rear. 

 This vessel (PL III, figs. 23 to 25 ; My.V.) arises on the dorsal 

 surface of the myel as far back as the 9th pair of spinal nerves. 

 After running along on the dorsal surface of the myel for a 

 short distance it separates into a right and a left myelonal vein. 

 Each of these vessels runs along the lateral surface of the myel, 

 passing between the dorsal and ventral roots of the spinal 

 nerves, finally terminating by emptying into the posterior en- 

 cephalic vein. Along its cephalic course the myelonal vein 

 receives numerous vessels from the myel, and sends across 

 dorsal connecting branches, which unite with the correspond- 

 ing vein on the opposite side. Although the myelonal vein 

 empties into the posterior encephalic vein, still, not all of its 

 blood reaches the jugular through that vessel, but some of it is 

 carried off by the first 3 spinal veins (Pis. II and III, figs. 

 16 and 24 ; Sp.V.). These vessels pass out with each alter- 

 nate pair of spinal nerves, and emptying into the neural veins, 

 which in the case of these anterior veins penetrate the dorsal sur- 

 face of the head kidney, and here break up into ver}^ small 

 veins, which again become collected into vessels that empty 

 into the jugular vein. The posterior encephalic vein is simply 

 a modified spinal vein, which after leaving the skull through 



