82 GEORGE L. STREETER 



ascertain very definitely the relations of the structure with which 

 we are concerned. 



A camera lucida drawing of the endolymphatic plexus and its 

 connecting vessels is shown in figure 5, as they are seen in the 

 cleared specimen mentioned above. In the same drawing is 

 introduced a profile reconstruction of the endolymphatic append- 

 age prepared from serial sections of the other labyrinth. From 

 an examination of this figure it will be seen that the endolym- 

 phatic appendage is divisible into a duct and a sac. The duct is 

 further divisible into a proximal flaring portion and a narrow por- 

 tion that connects this with the sac. It can be seen in sections 

 that the proximal flaring portion possesses thin walls that show 

 a tendency to be thrown in folds. The endolymphatic sac con- 

 sists of a flattened blind pouch with a rounded contour. Micro- 

 scopic examination shows that its walls consist of a single layer 

 of cuboidal epithelium which is uniform throughout the sac 

 except at its distal extremity where it narrows into a tubular 

 process whose epithelium retains the embryonic character. In 

 its general topography the endolymphatic sac maintains its former 

 relations and its distal part is found overlapping the dorso- 

 median wall of the transverse sinus. 



On examining the endolymphatic plexus in figure 5 it will be 

 seen that it has undergone certain changes as compared with the 

 younger stage shown in figure 4. A vascular plexus still envelops 

 the appendage everywhere. This consists of a thin walled endo- 

 thelial network whose meshes vary in size and pattern and lie 

 closely against the epithelial wall of the appendage. In the 

 drawing only the more prominent loops are shown; besides these 

 there are everywhere small anastomosing capillaries that inter- 

 vene between them. The network as a whole is richer over the 

 sac and over the proximal flaring portion of the duct and is more 

 scant over the narrow portion of the duct. Running through 

 the plexus there are a few larger channels that have been sepa- 

 rated out. These form main drainage channels that become 

 partially detached from the general plexus, though the latter con- 

 tinues to anastomose with them at frequent intervals. One of 

 these is the so-called 'vena aquaeductus vestibuli.' This forms 



