364 



SCANDINAVIAN KISHKS. 



dorsal and anal fins bepii to develop True i-iys; and 

 linally the knol)-like rudiments of the ventral tins a|)- 

 pear. Up to no-\v tiie head has been pert'eetly sym- 

 metrical. The eyes are ]ierfect, with strong niotory 

 muscles, and ha\'e already begun to show that marked 

 mobility whicii ciiai'acterizes the Flatfisiies in general, 

 one eye lying on each side of the tumid middle bi-ain. 

 The covei'ing bones of tlie 1)rain-case ai'e as yet mere 

 membranous rudiments. 



As the vertical fins now develop more and more, 

 the caudal fin assumes its homocei'cal sliape, the dorsal 

 and anal fins are furnished witii tiaie rays and inter- 

 spinal l)ones, and the bod^' gi'ows deeper. The young 

 Flatfish now begins to lie oftener on one side, and 

 swims in a more and more oblique ])Osition. (^ne of 

 the eyes begins to ttirn inwards, first moving some- 

 what forward to\\'ards the snout and inward toAvards 

 the opposite side of the body (fig. i)9, /y, <: and d), 

 then up the forehead and over to the op]>osite side 

 (fig. 99, e), and finally, in most cases, furtlier and 

 further back on this side, which is now the ei/c side, 

 while the other side (jf the body has become the l/liiid 

 ■■^ide. Sometimes, e. g. in the genus PInfopliri/s {BJioiii- 

 boidichtJi/fs), the eye retires so far back that it ap])ar- 

 ently lies high up on the occiput. 



Meanwhile the covering Ixjiies of the skull have 

 begun to develoj), but they are still cartilaginous and 

 thin, and of far too soft texture to hinder the move- 

 ments and the changes in the position of the eye, 

 whicIi, on the other hand, both ii\ the eventual sliajie 

 of tiiese bones and leave room for their abnormal, se- 

 condary development. In the first ))lace the front part 

 of tlie frontal bones (fig. 100, /' and /') is compressed 

 between the eyes (o and a'), while the posterior |)a.rt 

 of these bones (fig. 101, fr. d and fr. s, beneath in 

 the figure) generally retain their breadth, but grow 

 more ami more distoi-fed. The lateral ethmoid bones 

 (the anterior frontal bones, fig. 100, « and r/; fig. 101, 

 fr. (I. d and fr. ii. s), which are pierced by the olfactoiy 

 nerves, are also removed and changed in developiiient: 

 the lateral ethmoid bones of the blind side (fr.d.s) 

 and the tiaie ethmoid lione (tig. 100, c; in fig. 101 not 

 specially marked, but King between /'/•. a. .s and /V. ^^(/) 

 form the usualh- raised, aiitci'ior and antero-cxterior 



wall of the oi'bit, which is entirely closed on the outer 

 (u|)])er) side, this being due to the fact that the frontal 

 bones of the blind side {fr. ft) outside (al)ove) the eye 

 grow out anteriorly into a process which meets a C(jr- 

 responding excrescence in a backward direction of the 

 lateral ethmoid bones of the blind side. Sometimes, 

 however, these processes distinctly represent the sub- 

 orbital bones". They thus form an osseous bridge at 

 the eventual dorsal edge of the head; and forward above 

 this bridge, in most cases, grows tlic anteiaor part of 

 the dorsal fin with its interspinal bones, which are 

 supported thereon, just as the lateral nuiscles of the 

 bocU" (the occipitid nuiscular part) extend forward to 



Fig. 100. Skull <if a Cod, seen from above and reduced in size. 

 After Steexs'iTiUP. c, vomer; p, etiimoid bone; a right, a' left lateral 

 ethmoid bone; o, situation of the light, o' of the left eye; /', right, 

 /" left frontal bone; /), posterior frontal bone on the right, p' on the 

 left; t', upper occipital bone. 



this jioint. The occipital ridge of the skull is also 

 continued in most cases on this osseous bridge, which 

 thus, although secondary, and issuing from the original 

 later;d |)ai'ts of the skeleton, accjuires the appearance 

 of a median formation. It is true that the passage of 

 the eye exercises some influence over the position and 

 form of the other l)ones of the skull: the parasphenoid 

 bone anteriorly, from the orbital region, becomes more 

 or less twisted, or more developed on the one side of 

 the body (the blind side), and in most cases the vomer 

 also shares this rotation. Hut the bones of the true 

 cranium (exce]>t the frontal bones) undergo oid\' slight 



" In Pleiironectet! ryiioi/hs.iiis the osseous liridge thus formed is furnished, on the blind side, with a coarse-meshed network c^f bony 

 ridges, belonging to a nuiciferous duct; and in iSolea {Achini.f) lineata the bridge is double. The only other trace of a true suborbital ring 

 that occurs, is the frequent presence of a preorbital boue united to the latcial ethmoid bone of the eye side. 



