The Latero-Sensory Canals and Related Bones in Fishes. 457 



liowever definite]}^ given, and it may be tliat it lies in the hind end 

 of the squamosal, as it will be shown to do in Hippoglossus , the 

 posterior supratemporal ossicle then being a lateral extr^scapular. 

 The innervation of org-an 15, on the eyeless side of Pleuronectes, is 

 said to be by the "ramus supratemporalis X", while on the ocular 

 side it is by the ramus oticus, this latter innervation being a marked 

 departure from what is known in other fishes. 



After leaving this so-called posterior supratemporal ossicle the 



« 



canal is said to at once enter the pterotic (squamosal) and to there 

 immediately receive the hyomandibular (preopercular) canal. The 

 canal is then said to traverse the remaining portion of the pterotic 

 (squamosal) and then the sphenotic (postorbital ossification), and on 

 leaving the latter bone to enter the frontal, where it anastomoses 

 with the supraorbital canal. After this last anastomosis the main 

 infraorbital turns sharply downward and traverses a "chain of slender 

 suborbital ossicles, the posterior of which are sometimes called the 

 postorbitals, and the last of which is attached to the frontal". 



In the section of canal that is included between the points where 

 it anastomoses with the preopercular and supraorbital canals there 

 are said to be two sense organs, both of which are innervated by 

 the oticus. The posterior of these two organs certainly lies in the 

 squamosal. The anterior one would seem, by comparison of the 

 several figures, to lie in the frontal, and it is, as will be shown be- 

 low, found in the frontal in both Hippoglossus and Rhombus. The 

 sphenotic (postorbital ossification) of Pleuronectes thus probably does 

 not lodge a sense organ, and the section of canal said to be enclosed 

 in the bone must therefore be secondarily so enclosed. Wishing to 

 satisfy myself regarding this I have had two skulls of Pleuronectes 

 platessa prepared, one of them being about one-half the length of the 

 skull shown in Cole and Johnstone's figures and the other about one 

 third the length. In the larger skull, the sensory canal, as it traverses 

 the sphenotic (postorbital ossification), simply lies in a deep groove 

 on the dorsal surface of that bone. In the smaller skull it has a 

 similar relation to the bone on one side of the head, but on the other 

 side it is enclosed in the bone for about one half its length. It is 



