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from before backwards we find that the tube enters the anterior end of the tunnel on 

 each scale and passes through the aperture in the floor of the tunnel to enter the 

 tunnel of the next scale, and so on. But before passing through the aperture in the 

 floor of the tunnel the tube gives off a branch which continues to run through the 

 tunnel to its posterior aperture, and passes beyond the scale to open by a pore on the 

 surface of the skin. Thus corresponding to each scale of the lateral line there is a 

 pore in the skin which leads into the dermal tube of the lateral line. The course of 

 the tube and its relation to the scales are exliibited in Pig. 6, PI. XIV, which 

 represents an ideal longitudinal section of the skin along the lateral line : sc. indicates 

 the scales in section, d.t , the tube, p, the external pores. The left end of the section 

 is the anterior. On tlie inner wall of this lateral dermal tube are a number of sense- 

 organs supplied with branches of the nervm lateralis, which in the sole as in the 

 majority of fishes is a branch of the vagus. If we follow the lateral dermal tube 

 forwards we find that at the side of the back part of the skull, over the parietal crest, 

 it becomes separate from the skin and enters the hinder branch of a triradiate bony 

 tube : one branch of this bone passes straight forwards for a short distance and then 

 terminates, and the lateral tube then enters a tube in the pterotic bone. This tube 

 excavated beneath the surface of the bones of the skull is continued forwards, sometimes 

 opening into a groove on the lateral ridge of the skull : it passes just above the 

 posterior corner of the sphenotic bone, and then enters the outer edge of the posterior 

 half of the frontal ; then it is continued as an enclosed tul)e through the interorbital 

 process of the frontal, and emerging from this enters a separate tubular bone similar 

 to that wliich lies on the outer surface of the parietal crest. This bone bifurcates each 

 branch ending in the skin, probably by an opening to the exterior. This last bone is 

 the nasal : the former may be called the supra-temporal bone. {See Fig. A on the 

 following page.) 



It follows of course from the peculiar modification of the frontal bones that the 

 cephalic portion of the lateral tube on the left side, following the course of the left 

 frontal bone, passes from the apparent left side of the head to the right : morpho- 

 logically of course it retains its proper relations, but as it passed originally dorsal to 

 the left eye, it has been pushed over by the movement of that eye to the right side, 

 and so comes to lie to the right of the anterior part of the dorsal fin. But the left 

 nasal bone is on the left side, for the tube after leaving the left frontal bone bends 

 beneath the anterior dorsal interspinous bone, to the left side of the snout : thus the 

 left nasal bone is attached to the skin in front of the nasal capsule of the left side. 

 The right nasal bone lies in front of the nasal capsule of the right side. 



The supra-temporal bone, besides its posterior and anterior openings, has two others, 

 a dorsal and a ventral. The dorsal opening is at the end of a short branch, and leads 

 into a tube in the derma surrounded by modified scales, and in all respects resembling 

 the tube of the lateral line : this supra-temporal dermal tube in fact lies under and is 

 the cause of the supra-temporal branch of the lateral line described with the external 



L 2 



