ANATOMY OF VERTEBRATES. 117 



nasal bones. The arch is completed by the maxillary and pre- 

 maxillary bones, the symphysis of the latter forming its apex ; 

 and it is inclined forward, nearly or quite parallel with the base 

 of the skull ; which, in most fishes, extends 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 de- 

 pendent, circumscribing below the nasal or respiratory canal. The 

 pterygoid bones project backward and outward as the appendages 

 of the palato-maxillary arch, ib. 23, Both maxillary and intermax- 

 illary bones tend by their peculiar developement and independent 

 movement in bony fishes to project freely outward, downward, and 

 backward. 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 mentioned. 



The palatine (pleurapophysis of nasal vertebra, figs. 81, 84, 20) is 

 an inequilateral triangular bone, thick and strong at its upper 

 part, which sends off two processes : one is the essential point of 

 suspension of the palato-maxillary arch, and articulates with the 

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

 and passes forward to be articulated to a concavity in the superior 

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

 joint. In the Parrot-fishes and Diodons the articulation is quite 

 analogous to that of the mandible below with the tympanic pedicle. 

 In the Lepidosteus, Amia, and most Ganoids, it is by a suture. In 

 the Shad the palatine articulates with the premaxillary as well as 

 the maxillary. In the Mormyrus the palatines meet, and unite 

 together at the median line. The posterior border is joined to 

 the entopterygoid, fig. 84, 23, and its outer angle to the pterygoid. 

 The palatine contributes to form the floor of the orbit and the 

 roof of the mouth ; in many fishes it supports teeth, but is eden- 

 tulous in the Cod. It varies much in form in different species ; is 

 slender and elongated in the wide-mouthed voracious fishes as 

 the Pike, and is short and broad in the broad-headed, small- 

 mouthed fishes. 



The maxillary (hremapophysis of nasal vertebra, fig. 81, 21) is 

 usually a small edentulous bone, 1 concealed in a fold of the skin 

 between the palatine and premaxillary : it lies, in the Cod, fig, 

 75, 21, posterior to and parallel with the premaxillary, 22, which it 

 resembles in form, but is longer and thinner in most osseous fishes ; 



1 The Os mystaccum of ichthyotomists. 



