VASCULAR DRAINAGE OF ENDOLYMPHATIC SAC 8/ 



dura are found mmierous blood vessels which are shown in the 

 drawing as white spaces. The largest of these is transverse sinus. 

 A portion of its wall is missing having been injured in the removal 

 of the dura from the bone. Around the endolymphatic sac is a 

 thick plexus of thin walled veins which apparently is the same as 

 the endolymphatic plexus which we have studied in the younger 

 specimens. At the caudo-lateral surface of the sac they open 

 into a large channel which in turn drains into the transverse 

 sinus. This is the channel that follows along the endolymphatic 

 duct and is known as the vena aqua^ductus vestibuli. Other 

 dural veins anastomose with it, but its primary communication 

 is with the venous plexus of the endolymphatic sac. As this 

 specimen did not include the intraosseus portion of the endo- 

 lymphatic appendage the proximal connections of these veins 

 could not be studied. 



SUMMARY 



From the above study of the endolymphatic appendage in 

 human embryos the principal features in its development, to- 

 pography and vascularization may be summarized as follows: 



The endolymphatic appendage makes its appearance at the 

 dorsal tip of the otic vesicle in embryos about 4 mm. long, where- 

 upon it rapidly enlarges, forming an elongated tube that extends 

 upward toward the chorioidal roof of the hind-brain. As it 

 does this it becomes differentiated into two subdivisions : the distal 

 half spreads out forming a broad flattened blind pouch, the saccus 

 endolymphaticus; the proximal half, the ductus endolymphaticus, 

 forms an elongated narrow tube connecting the distal part with 

 the remainder of the labyrinth. The main features in this dif- 

 ferentiation are completed in embryos 30 mm. long and at the 

 same time the topographical relations of the appendage have 

 assumed practically the adult conditions. 



A prominent factor in the topography of the endolymphatic sac 

 is its relation to the transverse sinus. The characteristic flat- 

 tened form of the sac and the establishment of the sinus are to be 

 seen at about the same time. From then on the sac always lies 

 with its flat surface applied against the median wall of the sinus, 



