80 GEORGE L. STREETER 



utricle and saccule. At this point it anastomoses with the 

 vessels of the vestibular part of the labyrinth. The vessels be- 

 longing to the vestibule and canals are more sparse; a portion of 

 the cochlea, however, seems equally as well provided as the 

 endoljTiiphatic appendage. It is to be remembered that we are 

 dealing with an injected embryo and the meshes of this plexus 

 are doubtless distended, so that the picture we obtain shows 

 them more prominently than would be the case in uninjected 

 material. The topography and communications of the endo- 

 lymphatic blood plexus are shown more completely in figure 4. 

 This is an outline drawing of the labyrinth and its blood-vessels 

 in a human embryo 54 mm. long (No. 458, Carnegie Collection). 

 The blood-vessels were injected with India ink and after fixa- 

 tion the head of the embryo was dissected and the desired portions 

 of it were dehydrated and cleared in wintergreen oil. Figure 4 

 shows the right labyrinth as seen in such a specimen. The in- 

 jected vessels in the region of the vestibulo-cochlear junction are 

 shown in solid black and also their continuation into the endo- 

 lymphatic plexus inclosing the endolymphatic duct. The con- 

 tinuation of the plexus toward the lateral sinus is shown in stipple. 

 In the region of the endolymphatic sac a part of the plexus is 

 represented as cut away. The greater part of the sac is also cut 

 away in order to expose more completely the outer leaf of the 

 plexus, that intervenes between the endolymphatic sac and the 

 sinus, and its characteristic communications with the sinus. 

 The sac is quite flat and when it is intact it corresponds in contour 

 to that portion of the plexus that has been left. The reader will 

 be able to form a picture of the whole apparatus by imagining 

 the rest of the sac back in- place and covered in by the inner leaf 

 of the plexus. 



From an examination of figures 2, 3 and 4, we see, therefore, 

 that in embryos about 50 mm. long the endolymphatic append- 

 age consists of a narrow duct that widens out into a broad flat- 

 tened sac that lies between the chorioidal membrane of the lateral 

 recess and the transverse sinus. It is separated from the former 

 by the dura and is separated from the latter by the endolym- 

 phatic plexus. This plexus consists of thin walled capillaries 



