166 GEORGE L. STREETER 



normal lateral canal it is poorly differentiated (fig. 28). In 

 this kind of a labyrinth after undergoing differentiation for a 

 short time the process ceases. After that the only further sign 

 of development is an increase in size, which thus produces the 

 dropsical appearance, such as is seen in figure 27. The section 

 is cut obliquely through the oral end of the lateral canal and the 

 anterior canal. This section was chosen because it shows the 

 macula and its nerve ganglion connection with the brain. The 

 anterior canal, like the crus commune, is only slightly separated 

 from the general vestibular cavity. The posterior canal is rep- 

 resented by a bud extending caudally from the region of the crus 

 commune, such as we have already seen in figures 20 and 26. 

 There is no definite sign of a lagena or endolymphatic appendage. 



Labyrinth XV: (figures 29 and 30) . The photograph shown in 

 figure 29 is taken from Series X 1 A, slide 6, row 3, section 8. 

 It passes through the oral end of the labyrinth, showing the endo- 

 lymphatic sac, the small anterior canal, and the oral end of the 

 lateral canal opening widely into the vestibule. As can be seen 

 in figure 30, the caudal part of this labyrinth is fairly normal. 

 The oral end is quite imperfect, the parts being small and not 

 properly differentiated. The anterior canal is only a pouch not 

 completely separated from the vestibule. The lateral canal has 

 a deep impression on its dorsal surface marking the beginning of 

 a separation. This labyrinth has not completely recovered its 

 normal posture. It is displaced forwards and is tilted partially 

 forward so that the endoljanphatic sac, instead of bearing the 

 usual relation to the chorioidal membrane, is opposite the mid- 

 brain and lies embedded in the prootic ganglion. Though con- 

 sidering its abnormal shape it is not far from having the normal 

 posture. 



Labyrinth XVL- (figures 31 and 32) . The photograph shown in 

 figure 31 is taken from Series X 4 B, shde 2, row 2, section 4. 

 The section passes through the endolymphatic sac, which in the 

 sections a little more caudal touches the chorioidal membrane in 

 the characteristic way. The section also passes through the crus 

 commune and the vestibule with the lateral canal opening into 

 it. The lateral canal is quite perfect, but the anterior and poste- 



