CUTANEOUS BRANCHES OF THE VAGUS. II3 



and the m. dilator operculi and here it breaks up into 

 several branches which spread out over the inner surface 

 of the latter muscle, (i) one extends cephalad and dorsad, 

 (2) one caudad and dorsad, (3) one caudad and ventrad, 

 and (4) one directly ventrad. Of these, all but the last 

 are undoubtedly cutaneous nerves. The first one 

 {pp. X. i) runs between the m. levator operculi and the 

 m. dilator operculi to the skin under the lateral line canal ; 

 the second one {op. X. 2) can be traced along the inner 

 surface of the m. dilator operculi for almost its entire 

 length (back to 700), from time to time giving off twigs 

 which break through this muscle to the skin of the dorsal 

 part of the operculum. It innervates the cutaneous area 

 lying between those supplied by the two caudal cutaneous 

 branches {cut. X. 2 and cut. X. j). 



The third branch {op. X. j) also runs back along the 

 inner surface of the same muscle, just dorsally of the 

 upper edge of the opercular bone and farther back along 

 the outer side of the dorsal surface of this bone between 

 it and the m. dilator operculi. It can be followed nearly 

 to the caudal end of this muscle (720) and finally passes 

 through it at its insertion on the opercular bone to end in 

 the skin of the dorsal part of the operculum. The area 

 supplied is ventral to that supplied by the r. cut. X. j. 

 This is an exceedingly delicate nerve, containing only 

 about ten fibres in all, and could not be traced with cer- 

 tainty even sections, but for the fact that the fibres are 

 heavily myelinated, being nearly as large as typical motor 

 fibres. Their cutaneous nature is, however, beyond 

 question. 



It is probably the intimate relation of the three 

 cutaneous branches just noted to the m, dilator operculi 

 which led Baudelot ('83) to describe branches of the oper- 



