SKULL 877 
median end of the Frontals. In the majority of birds the Nasals! 
fuse with the Frontal, Ethmoid, Maxiila and Premaxilla, 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 Premaxille, and is a modification that stands in direct 
correlation with the mode of feeding, and is consequently very 
variable in closely-allied groups.® 
The Preemaxilla (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 Premaxilla 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 fellow 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 bones induced Garrod in 1893 (see INrRopuCcTION) 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 
Premaxilla. 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 
Limicolx, excluding Gdicnemus but including Parra, Laridx, Alcidx, Ptcroclide, 
- Columbe, Turnices, Grues, including Eurypyya and Rhinochetus but not Psophia, 
Mesites and Ibis, An approach to the holorhine structure is present in some 
individuals of Platalea, and among Passeres in the Furnariidx. All schizorhinal 
birds are also schizognathous, of which more presently ; but the reverse is by no 
means the case. 
2 The flexible part commonly lies behind the nasal cavities, but in Zrochili 
and Scolopacidz 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. 
3 The joint is most developed in certain Psittaci, Striges, Caprimulgide, 
Anseres, Steganopodes, several Ciconix—for instance Tantalus, though not in 
Ibis ov Platalea,—Corydon sumatranus, and is more or less developed in many 
other birds, among them not a few Pringillide. 
