84 GEORGE L. STREETER 



along the borders of the endolymphatic duct. It may be regarded 

 as having a group of tributaries from the remainder of the laby- 

 rinth. These are numerically indicated in figure 5 as follows: 

 '3' is a vein draining the dorsal surface of the utricle from where 

 it curves around at the base of the crus commune to join the endo- 

 lymphatic system; '4' drains the plexus belonging to the medial 

 wall of the utricle; '5' drains the plexus of the posterior ampulla 

 and the adjacent posterior surfaces of the utricle and saccule; 

 '6' indicates a group of anastomosing vessels from the median 

 wall of the saccule through which it also communicates with the 

 cochlear system. Opposite the narrow part of the endolymphatic 

 duct these various channels are assembled into two vessels of 

 which the one along the posterior margin of the duct is the prin- 

 cipal one, and the one that persists as the v. aquaeductus ves- 

 tibuli. Tracing it upward we find it receiving large tributaries 

 from the plexus of the endolymphatic sac and at the same time 

 enlarging into a wide channel along the caudal margin of the sac. 

 In addition to the tributaries from the endolymphatic plexus it 

 receives several tributaries from the plexus underlying the sur- 

 rounding dura, such as '1' in figure 5. It empties into the trans- 

 verse sinus by one or two openings in conjunction with adjacent 

 dural veins. 



In describing this plexus and the vena aquaeductus vestibuli 

 it is simpler to think of the blood stream as flowing all in one 

 direction, that is, toward the transverse sinus. In reality it is 

 quite possible that, due to mechanical' conditions, the plexus of 

 the proximal part of the duct drains backward into the vessels of 

 the rest of the labyrinth and in common with them through the 

 veins of the cochlear aquaeduct. The natural drainage of the 

 sac, however, is toward the transverse sinus. Under these con- 

 ditions the narrow part of the duct is a 'divide' from which the 

 blood flows in both directions, and through the same v. aquae- 

 ductus vestibuli. 



