312 



GEORGE L. STREETER 



r(>ti('uluni \v]uM-(>))y adjiicoiit si)jiceis unite in the formation of 

 composite larger spaces. This process continues until there is 

 a single continuous space extending down along the cochlear 

 duct representing each scala and at the margins of each of them 

 there is developed a membranous arrangement of the reticular 

 cells which completely walls off the space from the surrounding 

 tissue. Tn these alterations in the reticular mesh and in the 

 formation of the surrounding membrane there is an active change 



IMPRESSIO STAPED 



■"""■^ y^ 



SACCUS ENDOL 

 C, S. SUP. 



SCALA TYMP. 



DUCTUS COCH 



IMPRESSIO ROTUND. 



SCALA TYMP. 



SCALA V&STIB. 



HELICOTRP'MA 



Fig. 8 Lateral view of a wax-plate reconstruction of the left membranous 

 labyrinth and the periotic spaces in a human fetus, 130 mm. CR length (Car- 

 negie Collection, No. 1018) enlarged 9 diameters. The caPtilagenous stapes was 

 removed from this model and the oval impression that it makes on the cistern 

 can be plainly seen. The cistern has spread over the top of the utricle and along 

 the lateral canal. The scala vestibuli extends to the tip of the cochlear duct 

 where it communicates with the scala tympani, thus forming the helicotrema. 



Fig. 9 Median view of the same model shown in figure 8. The oval impres- 

 sion on the proximal end of ths scala tympani corresponds to the fenestra coch- 

 leae. As yet there is no communication at this point between the scala tympani 

 and the subarachnoid spaces corresponding to the aquaeductus cochleae. The 

 spaces making up the cistern cover almost the whole of the utricle and saccule 

 excepting the places at which the nerves enter and a small part of the medial 

 surface near the attachment of tlio appendage. 



