28 NORR/S. [Vol. VII. 



extension of the parietes of the yesicle. The apex of this exten- 

 sion, rounded at first, becomes more and more pointed and 

 shows at its extremity a thinning of the wall, which finally 

 results in the apex consisting of a delicate membrane (Fig. 8). 

 This condition later disappears, and the funnel-shaped cavity of 

 the lagena becomes more rounded and its wall more uniform in 

 thickness (Fig. lo). The auditory ganglion lies in close con- 

 nection with this thinner portion of the lagena and the peculiar 

 condition of the apex of the lagena may be related to its pres- 

 ence. In its earlier stages the lagenar cavity appears merely as 

 a funnel-shaped extension of the main cavity of the vesicle. 

 The walls of the vesicle in this region consist of the thickened 

 sensory epithelium (Fig. 8), but no differentiation of lagenar 

 and saccular maculae is as yet to be detected. Gradually a con- 

 striction occurs, marking off the lagena proper from the sacculus. 

 As a result the lagena becomes an elliptical vesicle, its major 

 axis extending obliquely dorso-ventrally, opening by a wide 

 aperture into the postero-mesal portion of the sacculus (Fig. 14). 

 The walls of the lagena consist during the greater part of devel- 

 opment of thick columnar epithelium, and the latter is till near 

 adult life continuous with the sensory epithelium of the sacculus. 

 On the mesal wall of the lagena is developed the papilla acustica 

 lagenae. 



Pars Neglecta. — As the constriction separating utriculus 

 from sacculus reaches the mesal wall of the ear vesicle the ven- 

 tral side of the constricting fold {i.e. the side toward the saccu- 

 lus) becomes much thickened in a certain area. As develop- 

 ment proceeds there also occurs a slight outpushing of the wall 

 of the sacculus ventral to the thickened area. This slight 

 mesal extension of the saccular parietes is the pars neglecta 

 and its thickened dorsal portion is the macula acustica neglecta. 

 At first the macula is continuous with the sensory epithelium 

 of the lagena and sacculus, but the ventral portion of the pars 

 neglecta gradually becomes thinner till it consists merely of a 

 delicate membrane closely connected with the perilymphatic 

 canal (Fig. 13). The macula ac. neglecta then becomes dis- 

 tinct. In the adult the pars neglecta is situated on the ventral 

 side of the utriculo-saccular constriction {i.e. it is a part of the 

 double fold of the constriction) posterior to the opening of the 

 recessus. As above noted, its macula is in early development 

 continuous with the sensory epithelium of the lagena. 



