ShIM'ELDT : OSIEOLOGY OK THE I I KRonit )NKS. 231 



are severally intended for. Each orbital cavity is then moderately 

 deep, its general shai)e being subhemispherical. Comparatively, 

 however, the orbit of this Ibis is not so deep, nor so thoroughly sur- 

 rounded by bony walls, as it is in Tantalus. A temporal fossa, as 

 seen on this lateral aspect of the skull in Plei:^adis is narrow, fairly 

 well deepened, and elongate in the antero -posterior direction. The 

 scpiamosal and postfrontal processes are small. The entrance to the 

 aural cavity is considerably shielded by the bony rim that surrounds it, 

 while we are to note that X\\q. foraineu oi'ale makes encroachment upon 

 its anterior precincts. lUit little importance distinguishes a quadrate 

 luvie. Broad and (piadrate in outline, its orbital ])rocess is squarely 

 truncated at its free inner extremity. 'I'here is a double facet upon the 

 mastoidal head, while the mandibular facets are but feebly carved out. 

 As compared with Tantalus, these latter are somewhat differently dis- 

 jjosed, especially the innermost one, it being markedly angulated in 

 the Ibis and strictly transversely placed in "Tantalus. Os quadratuni 

 in both genera possess a small hemispherical facet for articulation with 

 the proximal end of a pterygoid ; while the broad outer projection 

 presents upon its supero-external aspect the usual little pitlet for articu- 

 lation with the peg-like process on the inturned end of the proximal 

 extremity of the zygoma. It will be as well to say nere in passing 

 that the facets on the mastoidal head of the (juadrate bone in Tantalus 

 are much more distinctly separated than they are in Plegadis. 



Turning to the base of the skull we find the foramen magnum to be 

 of large size and subcordate in outline. In some specimens its supe- 

 rior margin is closely approached by the supraoccipital foramen upon 

 either side, lending to the postero-basic asi)ect of the cranium in this 

 region a very open appearance. The occipital condyle is very small 

 for a bird the size oi Plegadis, and it is seen to be sessile, with a faint 

 notch on its supero-niesial side. Immediately posterior to the aural 

 cavity, upon either side, there is developed a strong and distinct 

 descending paroccipital process — a character practically aborted in 

 Tantalus. Within these, and still further forwards, we observe small 

 circumscribed pits, one on each hand, that give passage to vessels 

 and nerves through foramina at their bases. The basitemporal area, 

 triangular in outline, is of fair size, while its anterior angle as a free 

 scale-like tip underlapping the openings to the F^ustachian tubes. 

 These are open channels for the best part of their extent in front, being 

 covered over only just before arriving at either aural cavity. 



