2S8 THE ANATOMY OF VERTEBEATED ANIMALS. 



Peristeromorphce, Clienomorphce, longer or shorter pro- 

 cesses extend from the basi-splienoid, and present terminal 

 articidar facets to corresponding facets upon the inner 

 sides of the pterygoids. These are hasi-pterygoid pro- 

 cesses, similar to those which occur in Lacertilia and some 

 OpMdia. 



The quadrate bone is almost always moveable upon the 

 skull, articulating with the pro-otic, alisphenoid, and 

 squamosal, by a single, or double, head. The distal head 

 articulates with the mandible below, the quadrato-jugal on 

 the outer, and the pterygoid on the inner, side. Hence, 

 when the ethmo-nasal joint is developed, any forward move- 

 ment of the distal end of the quadrate, such as must take 

 place when the mandible is depressed by the digastric 

 muscle, causes the maxillo-jugal bar to thrust the pre- 

 maxilla upwards and forwards; the palatine and pterygoid 

 bones, at the same time, sliding forward upon the rostrum 

 of the basisphenoid. Thus it comes about that the upper 

 jaw of such a bird as a Parrot rises, when, in opening the 

 mouth, the mandible is depressed. Each ramus of the man- 

 dible consists primitively of six pieces, as in other Sau- 

 ropsida, but the dentary pieces of each side axe, as in the 

 Chelonia, very early united, if indeed they are not ossified 

 from one centre. Very often, a fontanelle remains between 

 the dentary and the other elements, as in Crocodilia ; and 

 the dentary long remains readily separable from the rest ; 

 or, as in the Goatsuckers, is united with the others only by 

 fibrous tissue, so that it is moveable. The angle of the 

 mandible may be truncated or produced backwards into a 

 long curved process, as in Fowls (Fig. 82), Ducks, and 

 Geese. 



The hyoid is composed of basal elements, the anterior of 

 which, usually composed of two portions, lies in the tongue ; 

 and of two short, anterior, and two long, posterior, cornua, 

 which are never united with the periotic region of the 

 skull, and commonly remain quite free. In some of the 

 Woodpeckers, however, the long posterior cornua are im- 

 mensely elongated, and cm-ve upwards and backwards over 



