960 



PISCES. 



the muscles and other soft parts of this region 

 of the head. 



The Triglffi or Gurnards offer the best ex- 

 amples of the " hard-cheeked Acanthopterygii,'' 

 which owe their name to the following arrange- 

 ment of the above mentioned osseous pieces. 

 The first suborbitals are of enormous size, en- 

 tirely covering the face, articulating in front with 

 the bones of the snout, and posteriorly with the 

 preoperculum and two smaller suborbitals placed 



Fig. 492. 



Skeleton of Trigla tyra, showing the bones of the face and the pectoral 



Jin rays. 



at the posterior angle of the orbit. Its articu- 

 lation with the preoperculum is accomplished 

 by means of an immoveable suture, so that the 

 suborbital bones and the preoperculum must 

 move together. The upper part of the face, 

 moreover, is formed by the immoveable con- 

 solidation of the anterior frontals with the an- 

 terior extremity of the prsenasal bones, which 

 expand into a disc, and in some instances of 

 the voiner likewise, which is slightly visible 

 beneath the skin between the ossa nasi. All 

 these bony pieces, as well as those composing 

 the upper portion of the cranium, are hard, 

 granular, and often armed with spines and 



Fig. 493. 



cutting edges, so that few Fishes have their heads 

 so well defended against the attacks of their foes. 

 The Pleuronectidtf, or Flat-fishes as they are 

 commonly called, offer a most remarkable ex- 

 ception to the usual arrangement of the bones 

 of the face, which exhibits a want of symmetry 

 unparalleled in any other vertebrate animals. 

 In this family, which includes the Turbo t, the 

 Plaice, the Sole, and others similarly organized, 

 the whole trunk of the body is so much com- 

 pressed laterally that such fishes, 

 instead of swimming in the usual 

 position, lie upon their left sides 

 a circumstance which, added 

 to the singular fact that the right 

 side is equally coloured both up- 

 on the dorsal and ventral regions, 

 while the opposite is entirely 

 white, has given rise to the vul- 

 gar supposition that the white 

 surface is the ventral and the co- 

 loured the dorsal region of the fish 

 an error of which the anatomist 

 is immediately made aware by a 

 simple inspection of the skeleton 

 (Jig. 493). But in the construction 

 of the head, by a strange apparent 

 distortion of the elements com- 

 posing the face and cranium, both 

 eyes are allowed to be situated 



upon the right or upper surface of 

 body> Thig re ^ rkable resuU 



is entirely due to the suppres- 

 sion of those processes and bones on the left 

 side of the head which normally constitute the 

 orbital cavity, whilst on the right side they are 

 permitted to attain a very complete develope- 

 ment. The principal frontal bone (Jigs. 436, 

 437, 1, vol. iii. p. 826-7), which in all Fishes is 

 azygos, occupies its usual situation, but whilst 

 on the left side it is flat and bounded by a nearly 

 straight margin, on the right side of the mesial 

 line it presents as usual the processes which form 

 the roof and posterior boundary of the orbit. The 

 outer margin of the orbital cavity is formed by 

 one large bony piece, the representative of the 

 sub-orbital chain of bones, (Jig. 436, g g g) 



Skeleton of Hie Sole. 



