21 



almost complete loss of the left supraorbital sensory canal, 

 the anterior extremity of which it is its main function ic 

 protect.t The existence of the left nasal would of course 

 also be jeopardised by the motion of the intermaxillary 

 cartilage over the beak of the mesethmoid, which, whilst 

 not affecting the right nasal, would tend to reduce the left. 

 It is necessary to assume some co-operative cause such as 

 this, since the disappearance of a sensory canal does not 

 necessarily involve the reduction of the true lateral line 

 bones, or the Plaice would not possess a right lachrymal. 

 The nasal of the Plaice is a small semilunar bone attached 

 to the right side of the posterior vertical plate of the 

 mesethmoid. It supports the anterior extremity of the 

 right and only supraorbital sensory canal, and bounds the 

 right nasal sack internally. It is sometimes called the 

 turbinal. 



Lachrymal {R.Lc, L.Lc, figs. 1, 2, 3). — These have 

 been modified from the first of the suborbital series or 

 chain of lateral line ossicles supporting the infraorbital 

 sensory canal, and may hence be called the first sub- 

 orbitals. They have also been called the adnasal bones, 

 on account of their relations to the nasal sack. In the 

 Plaice they differ from the bones of the same name in 

 most Teleosts (including the Cod) in being closely 

 attached to the cranium. They differ in shape as shown 

 in fig. 1, the left being more concentrated than the right 

 (the latter best shown in fig. 3). The right lachrymal has 

 no connection whatever with the right infraorbital sensory 

 canal. Both lachrymals bound their nasal sack externally, 



fTraquair (loc. cit., p. 284) describes a "minute turbinal 'nasal] 

 ossicle" on the left side, supporting the "remnant of the main [supra- 

 orbital] canal of the eyeless side." We have found the latter in our sections 

 as Traquair describes it (see elsewhere), but not the rudimentary nasal. 

 Dr. Traquair's work, however, is so accurate, that he is doubtless correct in 

 this also. 



