THE LATERAL LINE ORGANS. 33 



Upon the reappearance of the canal in front of the 

 orbit (260), it sinks down into a deep groove in the lach- 

 rymal bone and at the level of the fifth infra-orbital sense 

 organ the bone arches up so as to entirely enclose the 

 canal. Between the fifth and fourth canal organs there is 

 no pore. Arising almost directly over the fourth organ is 

 the fourth pore of this series, which is directed cephalad. 

 There is a similar one over the third organ. The second 

 pore lies ventrally of the second organ and the first pore 

 dorsally of the same organ and a little farther removed. 

 Thus the number of pores corresponds to the number of 

 spaces between the organs, though they are somewhat 

 displaced from their normal positions. 



The infra-orbital canal terminates, after rising to the 

 top of the head and bending slightly caudad, in a pore 

 which lies near to and laterally of the posterior nasal 

 aperture and separated only by the latter from the supra- 

 orbital canal. It does not communicate with any other 

 canal system. 



S. — T/ie Supra-Orbital Canal. 



After separating from the infra-orbital, this canal sinks 

 at once into a groove in the frontal bone. It contains six 

 canal organs, all supplied by the r. ophthalmicus super- 

 ficialis VII. This groove at the level of the sixth organ 

 is roofed by a narrow bridge of bone and just cephalad of 

 this point is a narrow pore. The fourth and fifth canal 

 organs are close together and are roofed over by similar 

 narrow bridges of bone. The corresponding pore (fourth) 

 lies over the caudal portion of the fourth organ. The 

 third pore is longer, narrow and directed dorsad and 

 caudad. From this point forward the canal is wholly 

 enclosed by the frontal bone as far forward as the second 

 pore, which lies just behind the second organ. Somewhat 

 cephalad of this point (190) the frontal bone disappears, 

 its place as bearer of the canal being taken by the nasal, 

 in which the first organ of this canal lies. The first pore 

 lies just behind this organ and from this point to the end 



