THE LATERAL LINE ORGANS. 3I 



of which are innervated from the truncus hyomandibu- 

 laris, the latter from the r. mandibularis externus VII. 

 The groove in the preopercular bone is much deeper in 

 the vertical than in the horizontal limb and for a small 

 part of its course the bone entirely encloses the canal, 

 forming an osseous canal. 



There is no pore between the seventh opercular canal 

 organ and the main canal. The pore between the sixth 

 and seventh organs {p.p. 6, Fig. 5) passes dorso-caudad, 

 the fifth and fourth pores pass ventro-caudad, and are 

 rather longer than the sixth. Between the third and 

 fourth organs the canal again lies close to the surface and 

 the pore is a mere break in the outer wall of the canal 

 with no considerable tube. The first and second pores 

 are similar to the third. For an illustration of a typical 

 arrangement of these pores see Fig. 27. 



The opercular canal extends cephalad to 290, always in 

 the groove of the preopercular bone except at the ex- 

 treme cephalic end. After leaving this bone the canal 

 almost immediately comes to the surface, opens out and 

 disappears. 



6. — The Mandibular Canal. 



The mandibular canal appears less than one millimetre 

 in front of the cephalic end of the opercular canal (235) 

 and its course is a direct continuation of that of the oper- 

 cular canal. It im.mediately sinks down into a groove in 

 the articular bone by which it soon becomes entirely en- 

 closed. There are five organs in the mandibular canal, of 

 which the fifth lies in the articular bone, the others in the 

 dentary. They are all innervated from the r. mandibu- 

 laris extenius VII. 



About midway between the fifth and fourth canal 

 organs is the fourth mandibular pore. The third pore 

 lies nearer the third organ and the second pore nearer the 

 second organ, while the first pore arises almost directly 

 over the first organ. The mandibular canal ends in a 

 pore at the extreme tip of the mandible without communi- 

 cating with the canal of the opposite side. 



