VASCTTLAR DRAINAGE OF ENDOLYMPHATIC SAC 71 



duct does not form until after or just at the completion of the 

 detachment of the ear vesicle. In other words the separation 

 point of the ear vesicle is a variable one and is not to be con- 

 fused with the question of the homology of the endolymphatic 

 duct. As regards the latter, Krause concludes that the endo- 

 lymphatic duct of higher vertebrates is completely homologous 

 with the canal that connects the lab.yrinth in Selachians with 

 the surface of the head. 



This, in brief, is the present status of our information regard- 

 ing the endolymphatic duct in its general embryological aspects. 

 As to its histology and blood supply we are primarily indebted 

 to Boettcher '69. This investigator made razor-serial sections of 

 the endolymphatic appendage of the adult cat and new-born 

 babe. He, first of all, established the fact that it does not de- 

 generate in mammals as was thought by contemporary investiga- 

 tors, but develops further and persists through life as an epithelial 

 canal that connects with the two vestibular sacs, and forms an 

 important part of the labyrinth. The terminal part spreads out 

 (new-born babe) into a flattened sac 0.6 mm. wide, and is em- 

 bedded in the connective tissue of the dura. This sac he de- 

 scribes as made up of cuboidal pavement epithelium, closely 

 under which, and sometimes resting directly against it, are found 

 capillary loops filled with red blood cells. The walls of the sac 

 are somewhat irregular, due to the presence of small epithelial 

 pockets which project outward into the periosteum or bone, and 

 also papilla-like processes or folds which extend into the lumen 

 of the sac. Both varieties are provided with capillary vessels. 

 The capillaries are described as losing themselves in the perios- 

 teum. In another place he describes the small vessels of the ves- 

 tibular aqueduct at its bony exit as uniting to form a common 

 stem that empties into the inferior petrosal sinus. These signifi- 

 cant observations of Boettcher have received scant attention 

 from subsequent writers and do not seem to have resulted in 

 further investigation of these interesting. conditions. 



Hasse '73 to whom we owe the generally accepted terms 

 'endolymphatic duct' and 'endolymphatic sac,' and who con- 

 tributed many observations on the anatomy of the labyrinth, 



