xin 



PHYLUM CHORDATA 



415 



In many Carinataa, e.g. the Pigeon and the Fowl, the basi- 

 pterygoid processes are either absent or spring from the base of 

 the rostrum. The vomer is small and pointed, or may be absent, 

 and the palatines articulate 

 posteriorly with the rostrum. 

 The maxillo-palatines do not 

 unite with one another. 

 These peculiarities charac- 

 terise the schizognathous 

 arrangement. In the Pas- 

 seres a similar arrangement 

 obtains, but the vomer is 

 broad and truncated instead 

 of pointed in front. This 

 gives the cegithognathous 

 arrangement. Lastly in the 

 Storks, Birds of Prey, Ducks 

 and Geese, &c., the maxillo- 

 palatines (Fig. 1077, mx. p) 

 fuse with one another in the 

 middle line, often giving rise 

 to a flat, spongy palate and 

 producing the desmognathous 

 arrangement. 



The most specialised form 

 of skull is found in the 

 Parrots (Fig. 1078). In many 

 Birds the nasals and the 

 ascending process of the pre- 

 maxilla are very thin and 

 elastic where they join the 

 skull, and there is an unossified 

 space in the mesethmoid, so 

 that the upper beak is capable 

 of a considerable amount of 

 movement in the vertical 

 plane. In Parrots there is a 

 true joint between the upper 

 beak and the skull, allowing 

 of that movement of the 

 former which is so striking 

 in the living Bird. When 

 the mandible is depressed, 

 the contraction of the digastric 



muscle causes a forward movement of the lower end of the quadrate, 

 which pushes forwards the maxillo-jugal bar and the palatines and 

 pterygoids, the latter sliding upon the rostrum. Both the maxillae 



Oc.Cn. 



S.Oo 



FIG. 1076. Apteryx mantelli. Skull of young 

 specimen, from below. The cartilaginous parts 

 are dotted. B. Oc. basi-occipital ; B. pta. pr. 

 basi-pterygoid process ; B. TIH/I. basi-temporal 

 EC. Eth. ecto-ethmoid : Bus. T. Eustachian tube 

 Ex. Col. extra-columella ; Ex. Oc. ex-occipital 

 Int.. Car. carotid foramen ; Mr. maxilla ; A>. I 1 //', 

 foramen for facial ; .Yr. IX, X, for glossopharyn- 

 geal and vagus ; Nv. XII, for hypoglossal ; Oc. Cn. 

 occipital condyle ; Oc. For. foramen magnum ; 

 /''. palatine ; pa. oc. pr. par-occipital process ; 

 7'm.r. premaxilla ; Pt<i. pterygoid ; Qu. (orb. pr.) 

 orbital process of quadrate ; Qu. (ot. pr.) otic 

 process : Rout, rostrum ; N. Or. supra-occipital ; 

 S. Orb. F. supra-orbital foramen : >>'</. squamosal ; 

 Vo. vomer. (Alter T. J. Parker.) 



