VASCULAR DRAINAGE OF ENDOLYMPHATIC SAC 85 



ENDOLYMPHATIC APPENDAGE IN IvMBRYOS DURING SEVENTH 



MONTH 



To represent late fetal conditions of the endolymphatic sac, a 

 fetus was selected weighing 948 gms., in formalin, and measuring 

 240 mm. crown-rump length (No. 1131, Carnegie Collection). 

 The head of the fetus was removed and divided in bilateral halves. 

 On one side a dissection was made exposing the endolymphatic 

 sac which was done by carefully reflecting the dura. The form 

 of the sac and its relation to the transverse sinus was found 

 to be essentially the same as that shown in figure 5, so a draw- 

 ing of it will not be repeated. On the other side of the speci- 

 men the dura was raised in one mass together with all the soft 

 tissues between it and the bone ; this included the endolymphatic 

 sac, the periosteal vessels and part of the terminal portion of the 

 transverse sinus. This was then embedded and prepared in 

 serial sections, in a plane longitudinal to the duct and transverse 

 to the sac. A simplified drawing of one of these sections is 

 shown in figure (3. 



In the drawing the endolymphatic sac is shown in heavy black 

 stipple. It consists of a flattened sac embedded in the connec- 

 tive tissue that forms the substratum of the dura. Its distal 

 portion overlaps the dorso-median surface of the sinus as in the 

 previous stage. One new feature is found that was not present 

 in the younger stages and that is that the epithelial wall of the 

 sac projects irregularly in small longitudinal folds apparentl}' 

 thereby offering greater surface area. A characteristic fold of 

 this kind is cut through in the section shown in figure 6. Such 

 a fold gives the appearance of a double sac but tracing it through 

 the sections shows that it is only an out-pocket whose lumen 

 communicates with that of the main sac. 



The dura mater merges gradually into a somewhat loose sub- 

 stratum of connective tissue that attaches it to the bonj^ skull. 

 This is schematically represented in the drawing and the ragged- 

 ness of the bony surface of the dura is due to the difficulty in 

 detaching the dura from the bone and also in part to the irregu- 

 larity of the bone. In the meshes of the connective tissue of the 



