30 A''ORR/S. [Vol. VII. 



meet above the brain, antero-ventrally to the posterior border 

 of the cerebrum and ventral portion of the mid-brain, and pos- 

 teriorly as far as the glossopharyngeal nerve. Actual commu- 

 nication between the sacci occurs above the brain, but no coa- 

 lescence takes place below. As the cranial cartilages develop, 

 the saccus with part of the very slender ductus endolymphati- 

 cus comes to lie in the cranium, while the rest of the recessus 

 is in the otic capsule. From this time the saccus has the form 

 of a flattened bag lying in the subdural space. Its walls in the 

 adult stage retain their early cellular condition and are inti- 

 mately associated with vascular plexuses. I find no indication 

 of a communication between the cavities of the saccus and the 

 cranium such as was described by Hasse,i but such a communi- 

 cation may possibly occur, as the intricate inter-foldings of the 

 walls of the saccus with the pia render impossible any definite 

 conclusions from study of sections alone. 



The Sc7isory Epithelium. — As above described, immediately 

 after the formation of the auditory vesicle the columnar epi- 

 thelium shows on the postero-ventral wall a thickened patch 

 (Fig. 5). This pigmented area, by no means sharply defined from 

 the rest of the parietes, is the forerunner of the sensory patches 

 of the adult ear. As development advances, this area extends 

 toward the mesal wall, and in larvae of 12 mm. in length (Figs. 

 17 and 23) passes in the form of a band from the anterior part 

 of the vesicle destined to form the anterior ampulla in a latero- 

 ventral direction to the Anlage of the ampulla of the horizontal 

 canal, thence meso-ventrally across the utricular region to the 

 sacculus through the lagena, thence dorsally to the Anlage of 

 the posterior ampulla. The band is widest in the region of the 

 lagena. Although the sensory epithelium at this time forms a 

 continuous band, yet most of the future sensory patches can be 

 distinguished by the increased thickness of certain portions. It 

 is at this time that the lagena shows it apical portion, as a thin 

 membrane (Fig. 8). The division of the sensory band occurs 

 shortly after the differentiation of the semicircular canals, and 

 is threefold. The constriction that marks off the sacculus 

 from the utricular region at the same time isolates the portion 

 of the sensory area that later forms the posterior crista acustica, 



^ Die Lymphbahnen des inne'ren Ohres der IVirhelthiere, Anat. Studien, Heft 4, 

 1873. 



