Bones of the face.—The bones of the facial apparatus have likewise been pointed out and figured in the article above refeffed to. They consist, when the series is complete, of the fol lowing pieces, which, seeing the extremely vari ous forms of the face in this class of animals, present innumerable varieties as regards their developement and relative importance, notwith standing that their general arrangement is tole rably persistent throughout the class.
The maxillary (fig. 436, 18, vol. p. 826) and the intermaxillary (fig. 436, 17) form the anterior boundaries of the face and circumscribe the anterior and lateral limits of the mouth : the latter, however, is in Fishes the most important bone of the two, and is most comrnonly armed with teeth, while the former is very generally destitute of dental org,ans, arid being imbedded in the fleshy substance of the upper lip, has been called by some authors the labial bone or os mystacis. It is indeed upon the relative shape and size of the intermaxillary bone that the forrn of the upper jaw of Fishes principally de pends, and in some cases, as for example in the Sword-fish (Xiphias), Lepidosteus, &c. these bones are enormously prolonged anteriorly, so as to form an elongated beak or powerful ros trum which constitutes a formidable offensive weapon.
The face of Fishes, properly so called, is made up of several bony pieces very variable both in their size and number, which have been named the prenasal (fig. 436, 20,) the subor bital (fig. 436, g, g, g,) and the supra-temporal bones ; all of these, however, with the exception perhaps of the prxnasal, belong to the exoske leton (vide vol. iii. p. 845.) In the hard-cheeked Fishes (" joues cuirassees" of Cuvier) these osseous plates are enormously developed, and indeed form a kind of bony mask enclosing all the muscles and other soil parts of this region of the head.
The Triglw 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 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 naove 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 prxnasal bones, which expand into a disc, and in some instances of the vomer 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 cutting edges, so that few Fishes have their heads so well defended against the attack s of their foes.
The Pleuronectide, or Flat-lishes as they are commonly called, offer a most remarkable 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 Turbot, the Plaice, the Sole, and others similarly organized, the whole trunk of the body is so much pressed laterally that such fishes, instead of swimming in the usual —;.1— FUJitiVtly ur-ua "MIL MIL DILICJ —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 (fig.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 tue [apt or upper surface ot the body. This remarkable result is entirely due to the 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 ment. The principal frontal bone (figs. 436, 437, I, 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 straig,ht 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 lame bony piece, the representative of the sub-orbilal chain of bones, (fig. 436, g g g ) - which does not exist at all upon the opposite side of the head, while anteriorly the anterior frontals (2) and the nasal bone (20) complete this part of the face. An orbital cavity is thus constructed upon the right or upper side of the headof the Pleuronectid, which suffices for the lodgment of the two eyes, which thus take the only position in which both could be made useful.* Another equally remarkable arrangement is observable in the construction of the jaws of the Pleuronectidw, which are in many genera very unequally developed on the two sides of the median line, only in this case the prepon derance of developement is just the reverse of what exists in the orbital portion of the face, for here the bones of the right or upper side are small, while those of the left or inferior half are of considerably greater size and strength. Moreover, the former are but sparingly fur nished with teeth, while the latter support the thief part ,of the dental apparatus ; so that by this structure the mouth becomes twisted toward the ground, and the teeth so disposed as to work most effectually in that direction.