SPECIAL CUTANEOUS SUBDIVISION. 



133 



which grows gradually smaller and dwindles away toward the 

 caudal end of the acusticum. The smaller number of small 

 cells in the cerebellum and acusticum are of the form known as 

 cells of type II, whose neurites divide into terminal branches in 

 the near vicinity of the cell. A single granule cell is shown in 

 Fig. 39, and in Figs. 64 and 65 are shown the relations of the 

 granular and molecular layers in the brain of the sturgeon. In 

 cyclostomes the molecular layer extends along the lateral surface 



Plex.chor 



Fig. 66. — A transverse section of the medulla oblongata of Scyllium to show the 

 folding of the cerebellar crest and tuberculum acusticum. ac, tuberculum acus- 

 ticum; c.c, cerebellar crest; L.I.I., lobus lineae lateralis; L.v., lobus vagi. 



of the acusticum. In selachians there is a folding of the acusticum 

 in such a way that the molecular layer forms the floor of a 

 longitudinal groove on the lateral surface (Fig. 66) and in the 

 sturgeon this folding has gone so far that the groove has been 

 closed up by the fusion of the opposed surfaces of the molecular 

 layer. That part of the acusticum which lies above the fold is 

 the lohus lineae lateralis (Fig. 3) and in the sturgeon it is almost 

 separated from the rest of the acusticum by the cerebellar crest. 

 The large cells in the acusticum and cerebellum may be described 



