The Latero-Sensory Canals and Related Bones in Fishes. 461 



organ of the main infraoi'bital canal enclosed in the frontal bone, 

 the organ having a position in the canal, and an innervation, tliat 

 corresponds to that of the anterior squamosal organ of Amia, Lepi- 

 dosteus. Scomber and Conger. If it be the homologue of that organ 

 in those fishes, as seems so evident, its position in the hind end of 

 the frontal of Hippoglossus can be explained only by the assumption 

 that a latero-sensory ossicle which, in Amia and the three other fishes 

 mentioned, has fused with the squamosal to form the anterior part 

 of the dermal component of that bone, becomes, in Hippoglossus, fused 

 with the hind end of the frontal; and as I find the same arrangement 

 in Rhombus, and Cole and Johnstone describe it also in Pleuronectes, 

 it may be characteristic of the Pleuronectidae. In Hippoglossus, the 

 so-called lateral, or postorbital process of the sphenotic (postorbital 

 ossification) lies approximately opposite and ventral to the suturai line 

 between the frontal and squamosal bones, considerably posterior to, 

 and out of all direct relations to the eyeball. In Pleuronectes the 

 postorbital process has similar relations to the eyeball, but the 

 sphenotic has pushed upward between the frontal and the squamosal, 

 and separated those bones by a considerable interval. In Ameiurus 

 the bones here concerned have relations to each other, and to the 

 orbit, similar to those in Pleuronectes, but there is no infraorbital 

 organ in the frontal bone, the one otic organ that lies anterior to 

 the dorsal end of the preopercular canal lying between that canal 

 and the postorbital process, in exactly the position of the one ante- 

 preopercular otico-squamosal organ of Pleuronectes. The frontal otic 

 organ of the Pleuronectidae must then, in Ameiurus, have either 

 entirely aborted, or never have been differentiated as an independent 

 organ. In Conger, where the postorbital process also lies at a consi- 

 derable distance posterior to the orbit [5, p. 15], and has relations 

 to the frontal similar to those in Ameiurus and the Pleuronectidae, 

 there is an anterior otic organ that apparently corresponds exactly 

 to the frontal organ of the Pleuronectidae, but it is enclosed in an 

 anterior tubular prolongation of the squamosal, instead of in the frontal. 

 The right supraorbital canal of Hippoglossus begins, as Traquair 

 has stated, in the nasal (turbinai, Traquair) bone of its side. It then 



