o?i the Obliquity of Flounders. 369 



and thus actually through the vault of the cranium — is certainly 

 very remarkable, and, as the author admits, apparently beyond 

 all rule and analogy. We must therefore test carefully the facts 

 which are cited in its support. 



Two questions naturally arise : — first, Does the eye of the 

 blind side in the mature skull actually rest in an abnormal posi- 

 tion with reference to its essentially associated bones ? and se- 

 condly. At the period when the migration of the eye took place, 

 were the bones in such a position with relation to the eye as to 

 necessitate its reaching its final position by so unusual a course? 

 We agree with Prof. Steenstrup that the position of the eyes in 

 relation to their associated bones is essentially the same in all 

 the oblique heads of the Pleuronectidse. We shall select the 

 head of the Turbot {Rhombus maximus), a left-handed Flounder, 

 as an example. Placing the head on its side (PI. XVIII. fig. 1), 

 in its normal position in the living fish, two strong bony beams 

 connect the snout with the middle of the head; and between 

 these, as Prof. Steenstrup describes, lies the large round closed 

 orbit of the right eye. The left beam, which forms the partition 

 between the eyes, is made up principally of the thickened, con- 

 tracted anterior half of the left frontal bone (fig. 1 f). This is, 

 however, lined throughout its entire length by a strong sickle- 

 shaped process of the right frontal bone, and this process actu- 

 ally forms the left border of the orbit (fig. 1 /). Anteriorly and 

 externally the partition is strengthened for about one-third of 

 its length by an articulating process of the left prefrontal (fig.lfl'). 

 The right beam, forming the right border of the orbit, consists 

 almost entirely of the right prefrontal (fig. 1 a) enormously de- 

 veloped and synchondrosed with two strong ridges of the right 

 frontal, which, however, in this species, scarcely project in ad- 

 vance of the posterior edge of the orbit. In the Plaice {Platessa 

 vulgaris) they advance a considerable distance to meet the op- 

 posing process of the prefrontal. The left eye is in its ordinary 

 place beneath the outer edge of the left frontal, the left prefrontal 

 (as usual) merely eking out the anterior extremity of the upper 

 edge of its orbit. 



So far as its right frontal is concerned, the right eye is like- 

 wise in its normal position, at the outer edge of the sickle-shaped 

 process to which the anterior portion of the right frontal has 

 been reduced. 



So far the relations of the eyes to their associated bones has 

 not been disturbed, though an extraordinary shifting and absorp- 

 tion has taken place, which has removed nearly the whole of the 

 right half of the anterior portion of the right frontal bone from 

 the path of the right eye into its new position, and reduced it to 

 a thin crescentic plate. 



