ORIENTATION OF THE EAR VESICLE 25 



C III. Vesicle small. The wall is thick ventrally and composed of 

 high columnar cells. There is an especially thin part in the lateral 

 wall, suggesting the closed part of the vesicle. Several round cells 

 containing yolk granules are found in the cavity. Rotation is most 

 probably complete. 



D I. The vesicle is small and slightly oval. No significant difference 

 m thicloiess of the wall is to be recognized, but the ganghon, which is 

 closely attached to the medial wall, indicates the position of the vesicle. 

 Rotation is complete. 



D II (fig. 4). Vesicle is of medium size and in section oval. The 

 ventromedial wall is thick, the dorsolateral wall thin. The general 

 appearance gives every indication of a normally placed vesicle. 



D III. Vesicle oval in form. The lateral wall is thinner than the 

 medial; the wall is thickest ventromedially. Rotation is complete. 



Examination 18 hours after operation. 



A I. The vesicle contains a large cell mass in the lateral wall. The 

 whole structure is pathological. 



A II. The vesicle has three separate chambers. One is located 

 dorso-anteriorly, the second ventroposteriorly, and the third and 

 smallest, ventral to the first. The first two cavities are oval in shape. 

 There are two possibilities which might account for the formation of 

 such a structure: either the vesicle might have been severed in some 

 way at operation or the original vesicle may not have been entirely 

 removed, part of it remaining in position and fusing with the trans- 

 planted vesicle. The latter hypothesis, however, is rather doubtful, 

 since we know from the experiments of Streeter ('09) that two vesicles 

 do not fuse when placed in immediate contact. Since the structure is 

 abnormal, the posture cannot be determined. 



A III. The vesicle is small in size and oval in shape, the wall being 

 of uniform thickness throughout. The ganglion is attached to the 

 lateral side. The vesicle appears to be still in an inverted position. 



B I. Vesicle is small. Ventral wall is thick. Position chfficult 

 to determine. 



B II, The vesicle is too small to justify any conclusion. 



B III. Vesicle small. The thinnest part of the wall turns medially. 

 Probably no rotation has occurred. 



C I. The cavity of the vesicle is small, the lateral wall thick. No 

 rotation, or at most only partial rotation, is indicated. 



C II. Pathological. 



Examination 20 hours after operation. 



A I. No vesicle found. 



A II (fig. 5). The vesicle is large and of oval shape. The axis is 

 directed mediolaterally with medial inclination. The ventral wall is 

 thick. The ganglion is, attached to the ventromedial wall. Thus 

 rotation is in some measure complete. 



A III. The cavity of the vesicle is divided into two. The whole 

 structure is too abnormal to determine the position. 



B I. The vesicle is small. The cavity is divided into several parts. 



B II, Material incorrectly cut. 



