162 GENERAL OBNITHOLOGT. 



sents, certainly in part, probably in whole, the little bone of the middle ear called the malleus in 

 mammals. Anyhow this may be, the qnadrate of a bird bears the proximal ends of both jaws, 

 caiTying their final (posterior) articulation up to the squamosal and petrosal bones. Thus, the 

 foot of the quadrate forms the free hinge of the lower jaw, and also movably articulates the 

 back end of both the zygomatic and the pterygo-palatine bars or "arcades." The head of 

 the quadrate freely articulates with the squamosal, just in front of the tympanity cavity, which 

 it thus bounds in front; and there is usually a shoulder which furthermore articulates with 

 the anterior periotic bone, the prootic ; Struthious birds do not have these two distinct facets. 

 A long pedicle or orbital process extends forwards, inwards, and upwards in the orbit ; this non- 

 articular handle is for advantageous muscular traction. So circumstanced, the quadrate is a 

 stocky bone, of a shape reminding one of an anvil ; it rocks freely to and fro upon its cranial 

 socket, pulling and pushing upon the whole maxillary and mandibular mechanism, with such 

 effect that when the lower jaw drops, the zygomatic and palatal bars are automatically shoved 

 forward, tending to make the upper jaw rise, and so increase the opening of the mouth. Such 

 mobility of the upper jaw automatically with the movement of the lower is very free in parrots, 

 whose cranio-facial connections are quite articular in character ; it is well shown also in ducks ; 

 and probably nearly all birds have some such motion of the upper jaw upon the skull. In 

 nearly all birds, the mandibular articular facet of the quadrate is divided by a lengthwise 

 impression into inner and outer protuberances, or condyles, fitting corresponding depressions on 

 the articular face of the lower jaw ; in some birds the articular surface is single. The zygo- 

 matic articulation with the quadrate is made by the balled end of the quadrato-jugal socketed 

 in a cup at the outer side of the mandibular facet (with vaiious minor modifications in difierent 

 birds). The palatal articulation i^made by a little condyle of the quadrate, at the inner side of 

 the main facet, socketed into the cupped end of the pterygoid (with minor modifications). 



The Quadrato-jugal and Jugal Bones (Lat. jugvm, a yoke ; figs. 62, 63, 2, r; 69, 71, 

 si) 3) fo'^'^ most of the outer arcade -^ the jugal or eygomatie bar — leading from the quadrate 

 bone to the beak. The quadrato-jugal is posterior, reaching a variable distance foi"ward ; at its 

 fore end it is obliquely sutured to the jugal, a splint-rod which carries the bar forward to the 

 maxillary bone, with which it is in like manner obliquely sutured. The whole affair is almost 

 always a slender rod, which with its fellow of the opposite side forms the outermost lateral 

 boundary of the skull for a great distance. It corresponds in general with the " zygomatic 

 arch " of a mammal, which is made up of a " zygomatic process of the squamosal" and a malar 

 or " cheek-bone." The whole zygomatic arch, including the maxillary bone itself, is developed 

 from the outer part of the primordial pterygo-palatine bar (see fig. 65). In parrots the zygoma 

 is movably articulated before as behind. 



The Maxillary Bone (Lat. maxilla, upper jawbone; figs. 62; 63, s; 69, 71, 75, ma), 

 forming so much of the upper jaw of a mammal, is in birds greatly reduced, being starved out by 

 the predominant premaxillaries which form most of the upper beak. The shape of this stunted 

 bone varies too much to be concisely described. Its connections are, ordinarily, with the jugal 

 behind by a long slender splint-like process, and with the premaxiUary and usually the nasal 

 bones in front and externally. Internally, it may or may not connect with the palatal and 

 vomer. The zoological interest of this bone centres in certain inward (palate-ward) processes, 

 often its most conspicuous parts, and apparently corresponding to the plate which in a mammal 

 roofs the hard palate anteriorly. Though these are mere processes from the main maxillary, 

 they are so distinct and important that they are commonly described as if they were independent 

 bones, under the name of the matdllo-palatines. They are flange-like or scroll-like plates, or 

 large spongy masses of delicate bone-tissue, — endlessly varied in configuration and context (see 

 the various figures of base of skuU, mxp, beyond, where the palate-patterns are described). 



