Lect. II.] 



HINGING or THE LOWER JAW. 



39 



shows how this is done, and why the feat of fly-catching 

 is so difficult in the dog trying to sleep in the sun, but 

 kept awake by teasing flies. 



In the Duckbill, as in mammals generally, the pier 

 or hinge-piece is gone, and the maxilla inferior (or 



OS lO.S 



af '-V V ag 

 Fig. 4a. Fig. 4. 



Fig. 4. — Skull of Common Fowl {Qallus domxstious) cms-'Uaii larger than specimen. 

 •px, premaxiUary ; mx, maxillary ; v, vomer ; », nasal ; eth, ethmoid ; I, lacrymal ; 

 ^e, perpendicular ethmoid ; ps, presphenoid ; I, olfactory nerve ; io.s, interorhital 

 space ; os, orbitosphenoid ; /, frontal ; yf, post-frontal ; $, parietal ; «j, squamosal ; 

 s.o, superoccipital ; j,}i, jugal process of squamosal ; eo, exocciptal, V, 5th nerve ; 

 II, optic nerve ; ty.c, tympanic cavity ; H, basi-teraporal ; g, quadrate ; pg, ptery- 

 goid ; pa, palatum ; j, jugal ; qj, quadrate-jugal ; jJ.ap, posterior angular process ; 

 iap, internal angular process ; ar, articular ; ag, angular ; sa.g, supra-angular ; 

 d, dentary. 



FlQ. 4a. — Auditory Columella of Fowl, magnified 6 diameters, and shown from the 

 inside and end. 



mandible) is hinged directly to the temporal bone, a solid 

 part of the strong skull- wall. What has become of the 

 "OS quadratum," as the bird's jaw-pier is called? The 

 answer is, that in the mammal there takes place a 



'f^+e 



