3° NERVE COMPONENTS OF BONY FISHES. 



tance (660-675) ^s a wide shallow pore. There are no 

 pores in the main canal caudad of this point, nor in the 

 occipital commissure. 



4. — TJie Squamosal Canal. 



Cephalad of this point the main canal sinks down again 

 and is enclosed in the squamosal (pterotic) bone and in 

 this portion of the canal is included the single sense organ 

 of the main line lying between the occipital commissure 

 and the opercular canal {m. 2). This organ is innervated 

 from the r. supra-temporalis vagi. Farther cephalad the 

 canal comes to lie in a deep narrow groove in the bone up 

 to the point of union with the opercular canal. At this 

 point a rather long narrow pore is found, directed caudad 

 and ventrad close under the skin. 



After giving off the opercular canal, the main canal 

 (550) sinks again into a deep groove in the squamosal 

 bone and there is lodged the single canal organ of the 

 main canal between the opercular and the infra-orbital 

 canals (w. /). It lies nearer to the former than to the 

 latter and is innervated by the r. oticus. The canal runs 

 in this groove very nearly to the point where the infra- 

 orbital canal diverges from the supra-orbital, a tongue of 

 the squamosal bone running forward to accommodate it. 

 Here the canal communicates with the surface by means 

 of a pore. 



The operculo-mandibular canal is separated below the 

 eye into its two portions, opercular and mandibular, which 

 will be separately described, the canal organs and pores of 

 each being numbered from before backward. 



5. — The Opercular Canal. 



The opercular canal lies for almost its entire length in 

 a groove in the caudal and ventral faces of the preoper- 

 cular bone, which ventrally extends forward to the man- 

 dible. The canal has a vertical and a horizontal limb of 

 nearly equal length and contains seven canal organs, three 

 in the vertical and four in the horizontal limb, the former 



