20 CHIKANOSUKE OGAWA 



are situated at about the middle of the cell body. The lateral 

 wall is thinner, being formed by a single layer of cuboidal or low 

 columnar cells. By stripping off the skin the vesicle is usually 

 broken open in the fused area. Therefore, when the inverted 

 vesicle is found unclosed, as is generally the case a short time 

 after the operation, the open side should indicate the lateral 

 orientation in the original posture. There is, however, no clue 

 by which to distinguish the upper from the low^er side. 



The vesicle increases gradually in size, more so in its vertical 

 diameter, and presents an oval or pear-Uke form. The wall is 

 thickest at its ventral side and, as stated above, is formed of 

 high columnar cells, while the side walls, consisting of cuboidal 

 cells, are always thinner. In this stage the lateral wall is still 

 thinner than the medial. The upper dorsal part of the vesicle, 

 from which later the endolymphatic appendage develops, is com- 

 posed of somewhat higher cells. These constitute characteris- 

 tics which greatly facilitate the orientation of the operated vesicle 

 and serve as important criteria. As development proceeds, the 

 vesicle wall increases in thickness especially in the ventromedial 

 part. The relative difference in thickness between the medial 

 and lateral walls diminishes gradually, thus reducing its value 

 as a guide to the position of the vesicle. Sometimes the medial 

 wall may even be thinner than the lateral wall. Besides these 

 characteristics, the close connection between the acoustic of acial 

 ganglion and the medial wall affords a helpful clue to the posi- 

 tion of the vesicle. 



The above description concerns typical, normal development. 

 In exceptional cases, however, deviations from this course might 

 easily occur; for instance, in the early stages there may be little 

 or no difference in thickness between the medial and lateral 

 walls. Moreover, in judging the position of the vesicle, several 

 conditions must be kept in mind. Since an ear vesicle was 

 taken from one specimen and put into another, it is to be expected 

 that there would be some slight differences between the vesicles 

 of the normal side and the transplanted one. Furthermore, 

 when the vesicles are transplated they must first of all adapt 

 themselves to the new environment. For these reasons the 



