442 mb. e. w. l. holt — studies in [May 1 , 



of the head the disposition of the muscles was found to be almost 

 normal, the only difference being that the ventral face of the 

 anterior dorsal muscles, which normally exhibits an almost semi- 

 circular indentation for the reception of the dorsal hemisphere of 

 of the upper orbit, is, in the specimen before us, only slightly 

 concave in the same region. The space usually occupied by the 

 upper eye was filled with a mass of connective tissue, and to some 

 extent also by an extension of a pad of gelatinous and adipose 

 matter, which is always found above the right nasal organ. 

 Removing this, the right ectethmoid and the interorbital septum 

 have the usual appearance from this aspect, and the right orbito- 

 nasal nerve is seen passing as usual below the anterior notch of 

 the left ectethmoid. There is nothing in the condition of the 

 right orbital apparatus that calls for remark. The bony ridge on 

 the left edge of the top of the skull is, as usual, united to the 

 ventral face of the dorsal muscles, and to the great sickle-shaped 

 ligament-bone ' imbedded therein, by a very tough white ligament. 



The morphology of the Pleuronectid skull having been very 

 clearly defined by Traquair 2 many years ago, and that of the 

 Common Sole having received special attention in Mr. Cunningham's 

 monograph on that species, it is unnecessary forme to refer except 

 very briefly to the normal features of its component parts. In any 

 Flat-fish the top of the skull in the orbital region consists of two 

 bony ridges. Of these, that on the side of the fish occupied by the 

 eyes consists of the interorbital septum formed by the coalesced 

 anterior limbs of the two frontals (very unequally developed of 

 course) running forward to the ectethmoid of the ocular side. 

 The opposite ridge, that of the blind side, is the pseudomesial 

 process of Traquair, formed by the union of an anterior process of 

 the sphenotic of the blind side with a posterior process of the 

 ectethmoid of the blind side, and between these two ridges is the 

 upper orbital cavity, the optic nerve and oblique and recti muscles 

 thus reaching the eye. Accordingly in the normal Sole we find 

 the nerve and muscles of the left or upper eye to the right of the 

 pseudomesial process. 



In the abnormal Sole, as I have already mentioned, the eye is 

 not on the right side of this process, and in fact is completely shut 

 off from the right side of the head by the fibrous connection of 

 the process to the ventral face of the dorsal muscles. In fact, all 

 that is to be seen of the left orbital apparatus consists of the 



1 This bone, which supplies a firm base of attachment for the dorsal muscles 

 to the skull, is not found in Rhombus and Pleuronectcs, the genera to which the 

 observations of Cunningham and MacMunn limit the occurrence of the Cyclopean 

 malformation. It is possible that its presence in the Sole may supply the 

 wished-for structural peculiarity correlated to the non-occurrence of the 

 malformation in Solea, since, as the authors remark, the dorsal fin in Solea 

 actually extends further forward than in the Turbot, and much further than in 

 the Flounder, botli of which are commonly Cyclopean (see these authors, 

 op. cit. p. 806). It may be remarked, however, that the burrowing-habits of 

 the Sole might well preclude the survival of specimens so malformed, since the 

 longish dorsal hook would be a serious inconvenience. 



3 Trans. Linn. Soc. Lond. xxv. p. 263. 



