THE SKULL OF OSSEOUS FISHES. 105 



correspond with them and the neural arches, and are essentially four 

 in number in the osseous fishes ; viz. the ' palato-maxillary,' the 

 ' tymjiano-mandibular,' the ' hyoidean,' and the ' scapular.' Most 

 fishes have, likewise, appendages, which diverge or radiate from these 

 arches. A special (visceral) system of bony arches, called ' branchial,' 

 also persists in fishes, for the support and movements of the gills. 



Palato-maxillary Arch {fig. 30. h, iv, 20, 21, 22). 



I am induced to regard this as essentially one arch, from its con- 

 dition in the Lepidosiren and Plagiostomous fishes, and from the cir- 

 cumstance of its being completed or closed at one point only, viz. where 

 the premaxillaries meet or coalesce. The palatine bones are the piers 

 of this inverted arch, and their points of suspension are their attach- 

 ments to the prefrontals, the vomerine and the nasal bones. The arch 

 is completed by the maxillary and jiremaxiliary bones, the symphysis 

 of the latter forming its apex ; and it is inclined forwards, nearly or 

 quite parallel with the base of the skull ; which, in most fishes, ex- 

 tends to the apex of the arch, and in some far beyond it, being usually 

 more or less closely attached to it. In air-breathing Vertebrates the 

 arch is more dependent, circumscribing below the nasal or respiratory 

 canal. The pterygoid bones project backwards and outwards as the 

 appendages of the palato-maxillary arch. Both maxillary and inter- 

 maxillary bones tend by their peculiar development and independent 

 movement in bony fishes to project freely outwards, downwards, and 

 backwards. We find, at least, that the general form, position, and 

 attachments of the single and simple palato-maxillary arch, in the 

 Lepidosiren or Cestracion, are represented in most osseous fishes, by 

 their several detached bones, the names of which have been just men- 

 tioned, and which I shall now proceed to point out and describe as 

 they recede from the parts' of the vertebra to which they are sus- 

 pended ; taking as before the Cod-fish as the type. 



The palatine (pleurapophysis of nasal vertebra *, yf//. 30. 20) is an 

 inequilateral triangular bone, thick and strong at its upper part, 

 which sends off two processes ; one is the essential point of sus- 

 pension of the palato-maxillary arch, and articulates with the pre- 

 frontal and vomer at their point of union ; the other is convex, and 

 passes forwards to be articulated to a concavity in tlie superior 

 maxillary, to which, in all Fishes, it affords a more or less movable 



* To I'ojaniis belongs the merit of li.iving first enuiici. tetl tMs general liomo- 

 logical relation, in liis descrijition of tal). xii. fig. f 4. of his famous monograph. 

 " ()s palatiniim, seu costn corpori hnjiis vertebr.-u (athmoidalis sen capitis fjuart.-v) 

 ajipcnsa." (.tnatome Testiidinis Eurojxpo', i), 4 i.) 



