316 GEORGE L. STREETER 



corresponds to the fenestra cochleae (rotinuliini) and with which it 

 stands in intimate relation. 



In fetuses about sixteen weeks old the form and relations of 

 the scalae have nearly attained the adult conditions and this 

 represents the oldest stage studied in connection with the pres- 

 ent paper. The conditions found at that time are shown in 

 figures S and 9 which present median and lateral view^s of a 

 wax-jilate model of a human fetus 130 mm. CR length (Carnegie 

 Collection, No. 1018). On comparing the scala tympani and 

 scala vestibuli as seen in these figures with those in figures 6 

 and 7 it will be seen that they are larger in cross section and 

 more nearly cover in the cochlear duct. Furthermore they 

 noW' extend to the extreme tip of the duct and communicate with 

 each other across its central margin thus forming a helicotrema. 

 It will be noted that now^ even as far as the tip of the cochlea 

 each of the scalae consists of a continuous principal space. They 

 are however more mature and larger in their proximal portions. 

 Along the first turn of the cochlear duct they are w^alled off by 

 a smooth membranous margin w^hich separates them from the 

 adjacent reticular tissue. The spaces of the latter do not seem 

 to be taking any further part in the process of enlargement of 

 the scalae. Along the second turn of the cochlear duct, a 

 section of wiiich was shown in figure 1, the coalscence of 

 reticular spaces with each other and with the scalae is still in 

 active operation. This produces a greater irregularity of the 

 scalae than is shown in the model. The subsidiary spaces are 

 shown as a solid mass, the slender clefts separating them are 

 not represented. The nearer we approach the tip of the duct 

 the more immature are the scalae until the condition is reached 

 where the membrane-like margin is quite incomplete and the 

 spaces merge irregularly with the surrounding reticulum. Thus 

 a single specimen if studied in its different parts shows several 

 stages in this interesting process of the formation and growth of 

 the scalae. 



