150 GEORGE L. STREETER 



on account of the oblique position of the head, the large vein of 

 the head in the profile reconstruction shown in figure 1 neces- 

 sarily assumes a position that is more dorsal than it would be 

 in a true profile. In representing the veins only the principal 

 channels are drawn in; no attempt was made to trace the small 

 venules and their connection with the capillary plexus. Exami- 

 nation of the sections, however, shows that a capillary plexus 

 exists and closely invests the neural tube and the adjacent nerves 

 and sense organs. Minute anastomosing vessels can be seen con- 

 necting the plexus with the larger venous channels. 



"We thus have a simple system of drainage. The main channel 

 constitutes the primary head vein, a vessel consisting of a single 

 layer of endothelial cells. Its tributaries begin to unite in the 

 region of the diencephalon. In the region of the semilunar gan- 

 glion they have coalesced into a main channel that passes median 

 to the ganglion. Further caudal it is bent out of its course to pass 

 lateral and dorsal to the acustico-facial complex. It passes lat- 

 eral to the otic vesicle and the glossopharyngeal ganglion and then 

 bends inward to become median, and finally dorsal, to the gan- 

 glion nodosum of the vagus nerve, whence it passes down to empty 

 into the duct of Cuvier. The primary head vein receives every- 

 where many tributaries, chiefly ventral and dorsal. The ven- 

 tral ones are more numerous near the optic stalk and in the 

 neighborhood of the nerve-ganglion masses. The dorsal ones 

 may be classified in three groups; (1) an anterior group from the 

 region of the diencephalon and mesencephalon; (2) a middle or 

 cerebellar group in the region between the trigeminal nerve and 

 the acustico-facial complex; and (3) a posterior or occipital 

 group from the neighborhood of the vagus rootlets. Especial 

 attention is directed to these three dorsal tributary plexuses, as 

 their arrangement is significant for all the later stages, which 

 will presently be seen. 



As we pass to older stages, where the dura mater and the 

 arachnoid spaces are forming, we find that many of the anasto- 

 mosing channels between the capillaries of the brain and the pri- 

 mary head vein close off, and there is a general separation or 

 cleavage of the more superficial primarj^ head vein and its tribu- 



