SKULL 877 



median end of the Frontals. In the majority of birds the Nasals ^ 

 fuse with the Frontal, Ethmoid, Maxilla and Prsemaxilla, making 

 this part of the Skull more or less solid, though generally springy,"^ 

 but many birds possess a transverse fronto-nasal joint, often very 

 conspicuous and admitting of the vertical movement of what is 

 commonly known as the "upper mandible" of the bill. This joint 

 is just anterior to the Frontals and Lacrymals, but behind the 

 Nasals and Prsemaxillse, and is a modification that stands in direct 

 correlation with the mode of feeding, and is consequently very 

 variable in closely-allied groups.^ 



The Prsemaxilla (or Intermaxilla) is in Birds an unpaired bone, 

 its right and left component halves being fused from the beginning. 

 It forms the anterior and largest part of the so-called " upper 

 mandible," of which it is the most important factor, though the 

 outward shape of the BILL (p. 32) depends chiefly on its rhamphotheca, 

 and being therefore intimately connected with the bird's economy 

 is subject to very great variation in proportion and strength. Each 

 half of the Prsemaxilla sends out three processes — (1) one which 

 fuses with the Maxilla and forms the anterior part of the upper 

 jaw, (2) one which contributes to the formation of the anterior 

 part of the palate, and (3) one which together with its felloAv on 

 the opposite side forms the culmen (p. 33) and extends backward 

 to the Frontals. 



The paired Maxillaries form, as just stated, part of the upper 

 jaw, contributing also to the floor of the nasal cavity, and always 



1 The mutual relations of the processes of the Nasals to those of the neigh- 

 bouring boues induced Garrod in 1893 (see Inteoduction) to distinguish Birds 

 as HoLORHiNAL (p. 425) where the anterior margin of the Nasal is concave, and 

 SCHIZORHINAL (p. 816) where this posterior border of the nasal cavity is con- 

 tinued backward into a slit which extends beyond the frontal processes of the 

 Prgemaxilla. To use this feature as a primary taxonomic character is an error, 

 as he himself speedily saw, but otherwise it is as good as many others, though 

 closely-allied birds differ in this respect. The typically schizorhinal birds are the 

 Limicolse, excluding CEclicnemus but including Parra, Laridae, Alcidm, Pteroclidse, 

 Columhse, Turnices, Gnies, including Eurypyga and Ehinochetus but not Psophia, 

 Mesites and Ihis. An approach to the holorhine structure is present in some 

 individuals of Platalea, and among Passeres in the Furnariidse. All schizorhinal 

 bii'ds are also schizognathous, of which more presently ; but the reverse is by no 

 means the case. 



^ The flexible part commonly lies behind the nasal cavities, but in Trochili 

 and Scolopacidm far in front of the nostrils, so that only the anterior part of the 

 " upper mandible " is movable, and motion can be effected while the mouth is 

 closed. In some Plovers and Ibises, and probably a few other birds also, such a 

 flexible region exists beside the usual fronto-nasal one. 



^ The joint is most developed in certain Psittaci, Striges, Caprimulgidx, 

 Aiiseres, Steganopodcs, several Ciconise ■ — for instance Tantalus, though not in 

 Ibis or Platalea, — Corydon sumatranus, and is more or less developed in many 

 other birds, among them not a few Fringillidae. 



