78 GEORGE L. STREETER 



ENDOLYMPHATIC APPENDAGE DURING THE THIRD MONTH 



The topography and vascular drainage of the endolymphatic 

 sac in embryos about 50 mm. (crown-rump) long are shown in 

 figures 2, 3 and 4. In figure 2 can be seen the general posture of 

 the labyrinth and the relation of its component parts to the dural 

 sinuses. This figure is drawn from a profile reconstruction of the 

 labyrinth, dural veins and central nervous system in an embryo 

 50 mm. long (No. 96, Carnegie Collection). The reconstruction 

 was prepared by projecting the serial sections on transparent 

 papers which were then superimposed and all traced on one sheet. 

 It will be noted that the endolymphatic sac passes upward so 

 that its dorsal one-third rests against the median surface of the 

 transverse sinus, opposite the chorioidal roof of the ventricle of 

 the hind-brain. It does not project above the sinus as in the 

 younger stage shown in figure 1. 



A section through this region is shown in the accompanying 

 figure 3. This is a portion of a sagittal section through a human 

 enbryo 52 mm. long (No. 448, Carnegie Collection). Before the 

 embryo was prepared in serial sections its vascular system was 

 injected with India ink through the umbilical vein. This in- 

 jection mass is shown in the drawing in solid black. The section 

 passes antero-posteriorly through the lateral part of the cere- 

 bellum, and includes a portion of the ventricle with the chorioidal 

 villi projecting into it. At the base of the villi there is a col- 

 lection of the injection mass which apparently is an extravasa- 

 tion. This is separated from the endolymphatic sac and its 

 vessels by the dura which is already fairly well outlined, though 

 it is not represented in the drawing. 



The feature to which particular attention should be given is 

 .the capillary plexus surrounding the endolymphatic sac. Its 

 general character is indicated, and it can also be seen that it 

 drains by several outlets into the transverse sinus. On following 

 it through the sections of the series it is found that it completely 

 envelops the endolymphatic sac and duct. It can be traced cen- 

 trally within the cartilage as a finely meshed tubular covering of 

 the duct extending to the region where the duct arises from the 



