32 'Journal of Comparative Neurology and Psychology. 



fourth and fifth. In later stages it is joined and probably over- 

 lapped by the posterior spreading of the anterior mandibular 

 group. 



The third group (C) includes buds lying on the operculum 

 posterior to the preceding group. The buds lying in the region 

 of the pre-operculum are innervated by the fibers arising from 

 the main stem of the ramus hyomand. just before it divides into 

 the ramus mand. ex. VII and ramus hyoideus. The buds lying 

 on the dorsal and posterior portions of the operculum near the 

 post-frontal and squamosal are innervated by the ramus oticus. 

 This group appears somewhat earlier than those of the tw^o pre- 

 ceding subdivisions, there being 1 1 buds in series U, 9.4 mm. 

 Two of them are situated on the dorsal posterior portion of the 

 operculum between the first and second organs of the main lateral 

 line and nine along the area of the mandibular lateral line canal. 

 Of these nine one is between the seventh and eighth mandibular 

 lateral line organ and eight are between the last mandibular 

 lateral line organ and the first main lateral line organ and all lie 

 below the line of the canal. 



Of the 19 buds lying on the opercle in the 11 mm. embryo, 

 two lie between the fifth and sixth mandibular lateral line 

 organs. These two buds have been incorporated here but they 

 may belong to the quadrate group mentioned above. Of the 

 remaining 17, five lie between the sixth and seventh mandibu- 

 lar lateral line organs, and six lie between the seventh and eighth, 

 while two lie between the eighth mandibular and the first main 

 lateral line organs and four lie between the first and second of 

 the organs of the main lateral line. Of the six buds appearing 

 in the opercular group in the 14I mm. embryo, four lie between 

 the seventh and eighth mandibular organs and two between the 

 last mandibular organ and the first main lateral line organ. 

 There seem to be no buds on the posterior dorsal portion corre- 

 sponding to those between the first and second main organs in 

 the II mm. embryo. The deficiency of buds in this group in the 

 14! mm. embryo is quite striking. 



In Herrick's Ameiurus paper ('01) the ramus oticus is de- 

 scribed as innervating the dorsal portions of the operculum and 

 the post-frontal and squamosal bones. There seems to be no 

 way to separate this area from that of the buds appearing on 

 the pre-operculum, since membrane bones are not definitely 



