EXTERIOR PARTS OF BIRDS 



147 



assuming the functions of both lips and teeth, neither of which do 

 any recent birds possess. An organ thus essential to the prime 

 functions of birds, one directly related to their various modes of life, 

 is of much consequence in a taxonomic point of view ; yet its 

 structural modifications are so various and so variously interrelated, 

 that it is more important in framing genera than families or orders ; 

 more constant characters must be employed for the higher groups. 

 The general shape of the bill is referable to the cone ; it is the 

 anterior part of the general cone that we have seen to reach from 

 its point to the base of the skull. This shape confers the greatest 

 strength combined with the greatest delicacy ; the end is fine to 

 apprehend the smallest objects, while the base is stout to manipulate 

 the largest. Biit in no bird is the cone expressed Avith entire pre- 

 cision ; and, in most, the departure from this figure is great. The 

 bill always consists of two, the upper and the lower 



Mandibles (Fig. 26), which lie, as their names indicate, above 

 and below, and are separated by a horizontal fissure, — the mouth. 

 Each mandible always consists of certain 

 projecting skull-bones, sheathed with more 

 or less Iwrny integument in lieu of true 

 skin. The framework of the Upper Man- 

 dible is (chiefly) a bone called the 'inter- 

 maxillary, or better, the j^'^'einaxillar//. In 

 general, this is a three-pronged or tripodal 

 bone running to a point in front, with 

 the uppermost prong, or foot, implanted 

 upon the forehead, and the other two, 



lower and horizontal, running into the of upper mandible ; 6, culmen ; c, 

 • 1 n ,1 1 11 mi fv^ 1 1 f j_i nasal fossa; d, nostril; e (see be- 



sides of the skull. ihe scaffold of the low); /, gape, or whole commis- 

 sural line ; g, rictus ; h, commis- 

 sural point or angle of the mouth ; 

 (', ramus of under jaw ; j, tomia of 

 , . . , . . . under mandible (the reference 



shaped, AVlth the point or convexity in lines e should have been drawn to 

 r . 1 , 1 • , •, 1 _ inilicate the corresponding tomia 



front and the prongs running to either of upper mandible); /.-, angle of 



side of the base of the skull l)ehind, to gonys; ?, gonys ; m side of under 



' mandible ; n, tips of mandibles. 



be there movably hinged. These two 



bones, with certain accessory bones of the upper mandible, as the jxtlate 

 bones, etc., together Avith the horny investment, constitute the Jaius. 

 Both jaAvs, in birds, are movable ; the under, by the joint just men- 

 tioned ; the upper, either by a joint at, or by the elasticity of the 

 bones of, the forehead ; it is moved by a singular muscular and bony 

 apparatus in the palate, further notice of Avhich is given beyond, 

 under head of Anatomy (Osteology). The motion of the upper 

 mandible is freest and most extensive in the parrot tribe, Avhere 

 both fronto-maxillary and palato-maxillary sutures exist. "When 

 closed, the jaAvs meet and fit along their apposed edges or surfaces, 



Fig. 2(5.— Parts of a Bill, a, side 



Under Mandible is a compound bone 

 called inferior maxillary ; it is U- or Y 



