498 EMBRYOLOGY. 



auditory epithelium is distributed into an equal number of separate 

 patches, to which then the auditory nerve is distributed. Ac- 

 cordingly the auditory epithelium is resolved into a macula acustica 

 in the sacculus and another in the utriculus, into a crista acustica 

 in each of the ampullae of the semicircular canals, and into an 

 especially complicated termination in the ductus cochlearis. Here 

 the auditory epithelium grows out into a long spiral band, which is 

 known under the name of CORTI'S organ. 



Upon the separation of the auditory epithelium into maculae, 

 cristae, and organ of CORTI, the originally single auditory nerve 

 distributed to the auditory vesicle is likewise resolved into separate 

 branches. We distinguish in the case of the auditory nerve the 

 nervus vestibuli, which is in turn divided into numerous branches 

 distributed to the maculae and cristae, and the nervus cochleae. 



The originally single ganglion acusticum belonging to the auditory 

 nerve also becomes differentiated into two separate portions. The 

 portion belonging to the nervus vestibuli is in the adult located in 

 the internal auditory meatus far from the terminal distribution, 

 forming here the well-known intumescentia gangliformis Scarpae ; 

 the portion belonging to the nervus cochleae, on the contrary, 

 adjoins the terminal distribution of the nerve. In the embryo it 

 (figs. 277, 278 gc) is closely united with the fundament of the ductus 

 'cochlearis, and as the latter increases in size grows out to the 

 same extent in the form of a thin band, which reaches to the blind 

 end of the ductus and is known under the name of ganglion spirals 

 (fig. 283 gap). 



(b) Development of the Membranous Ear-Capsule into the Bony 

 Labyrinth and the Perilymphatic Spaces. 



All of the changes which have been mentioned hitherto have 

 proceeded from the epithelial vesicle which was constricted off from 

 the outer germ-layer. It is now my purpose to direct attention to a 

 series of processes which take place around the epithelial cavities, in 

 the mesenchyme in which they are imbedded. The processes lead 

 to the formation of the bony labyrinth, the perilymphatic spaces 

 and soft connective-tissue layers, which are intimately joined to the 

 purely epithelial structures hitherto treated of, and with the latter 

 are embraced in descriptive anatomy under the name of membranous 

 labyrinth. Changes take place here similar to those in the develop- 

 ment of the neural tube and of the eye, in which cases also the connec- 

 tive-tissue surroundings are modified in a special manner and with 



