146 STRUCTURE AND CLASSIFICATION OF BIRDS 



In the tinamous there are a series of these bones, which in 

 Psopliia are reduced to a smaller number, and in the passe- 

 rine Menura to three only ; 011 the other hand in Perdix 

 they are again more numerous. It is possible that in such 

 birds as Rhinochetus and (Edicnemus, in which the edge of 

 the bony orbit is very sharp, the thinness of the edge is due 

 to the fusion of a set of these bonelets with the true margin 

 o the frontal. As will be seen, the existence of these bones 

 is so rare as to render them of not great service from a sys- 

 tematic point of view ; but it is only 

 among birds which may be fairly 

 on other grounds regarded as 

 archaic that they are to be met 

 with. 



The occipital fontanelles (fig. 

 84) are mostly developed in water 

 birds, though any connection be- 

 tween them and the habit of the 

 birds is at least not obvious. They 

 are most general among the 

 Limicolse and the duck tribe, but 

 are found also in the Plataleidse 



and exist temporarily in the gulls ; they are also found in 

 the flamingo, Gruidse, and among the auks. 



Almost the same remarks may be made of the impressions 

 for the supra-orbital glands. They are very marked in the 

 Limicolse, being more usual than the occipital fontanelles ; 

 they are met with in the auks, divers, and penguins ; in the 

 cranes and Plataleidse they are present, but not so conspicuous. 

 The hinge line between face and skull is seen in its most 

 fully developed condition in parrots, where the face is actu- 

 ally movable on the head. But it is commonly met with 

 elsewhere, particularly among the Anomalogonatae ; it is 

 associated with holorhiny and with comparatively short 

 nasal processes of the premaxillary. 



Apart from their relations to the vomer the palatines and 

 ptenjyoids show some variations in structure. As to the 

 pterygoids, the most prominent difference concerns the place 



FIG. 84. SKULL OF 

 Magellanica. BACK 

 (AFTER GARROD.) 



VIEW. 



