LECT. II.] 



HINGING OF 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 



IO.S 



Fig. 4A. Fig. 4. 



FIG. 4. Skull of Common Fowl (Qallus domesticus) one-half larger than specimen. 



px, premaxillary ; mx, maxillary; v, vomer ; n, nasal ; eth, ethmoid ; I, lacrymal ; 



pe, perpendicular ethmoid ; ps, presphenoid ; I, olfactory nerve ; io.s, interorbital 



space ; os, orbitosphenoid ; /, frontal ; pf, post-frontal ; p, parietal ; sq, squamosal ; 



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



II, optic nerve ; ty.c, tympanic cavity ; bt, basi-temporal ; q, quadrate ; pg, ptery- 



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



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



d, dentary. 

 FIG. 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 

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

 answer is, that in the mammal there takes place a 



