88 Journal of Comparative Neurology. 



folds and forms an undulating lamella of considerable thickness 

 which forms the entire ventral and mesal wall of the lateral re- 

 cess. Figs. 4, 8, 29, 33. 35 and 36. 



At the cephalic portion of the recess the primary and sec- 

 ondary lips are indistinguishable and are closely fused with the 

 ectal surface of the restis and apparently enter into the forma- 

 tion of the lateral root and ganglion of the auditory. Compare 

 Figs. 30 and 34, human, with Fig. 14, a frontal section of the 

 brain of a pig embryo, twenty-one millimeters long, through the 

 auditory nerve and with Figs. 15, 16 and 38, dog. 



Cephalad the rhomboidal lip can be followed beyond the 

 pons flexure, where it becomes very pronounced in the region 

 of the cerebellum and probably gives rise in a large degree to 

 the lateral protons of that organ. Figs. 7 and 8. 



The connection of the rhomboidal lip with the auditory 

 tract or acusticum seems fairly well proven. The tuberculum 

 acusticum (dorsal nucleus) apparently corresponds to the fliigel- 

 wiilste, i. e. , primary bend of the rhomboidal lip, and as just 

 stated the ganglion of the lateral root is carried by the bending 

 of the lip over the restis. 



The comparison of this region in early embryos with the 

 acusticum in some fishes, is exceedingly interesting and sug- 

 gestive. The brain of Amia as figured by Kingsbury close- 

 ly resembles the early embryonic condition of the mammalian 

 brain in this region. The close connection in this form of the 

 cerebellum with this portion of the oblongata is emphasized by 

 him, which is of great interest when we consider that in mam- 

 malia, as already pointed out, the lateral portions of the cere- 

 bellum and the auditory region are probably formed from a con- 

 tinuous fold of the dorsal lamella, namely the rhomboidal lip. 



The excursion of the primary rhomboidal lip in the region 

 of the cerebellum, which is so marked in the human embryos, 

 has not so far been observed im embryos of the lower Mamma- 

 lia. Compare Figs. 6, 7 and 8 of the human embryos, with 

 Figs. 9, II, 12, 13 and 14 of the cat and pig. 



It is possible that it may be in more advanced embryos of 

 these forms. I have observed indications of it in slightly older 



