292 MR. W. K. PARKER ON THE OSTEOLOGY OF BAL^NICEPS REX. 



region. In the latter non-typical birds, e. g. Dromaius and Rhea, the process is obsolete 

 which in ordinary birds descends from the nasal to the maxillary ; and in Rhea the 

 broad single nasal process of the coalesced pre-maxillaries is unusually short, being 

 succeeded by the nasals, which here meet at the mid-line for some distance, divaricating 

 again as they pass, narrow and splint-like, between the large lacrymals. This meeting 

 of these bones along the mid-line is very exceptional in birds ; yet they really do 

 approach each other more nearly than would appear from a casual view of the matter. 

 In such birds as the Pigeon, the thin splint-like mesial and lateral processes form but 

 a small part of the bone, which, higher up, becomes cellular, meets its fellow, and 

 forms a large mesial oval part of the forehead, pushing the narrow anterior portions of 

 the great sphenoido-frontals aside. In birds with very cellular foreheads, — e. 7. the 

 Owls {Strix, Ulula, Asio, &c.), the Balearic Crane (Grus pavonina), the Woodcock 

 (Scolopax), — the thin tips of the pre-maxillaries pierce the bone of this frontal region, 

 wedging themselves in between the roof-bones and upturned centrum of the anterior 

 sphenoidal cincture. But the nasals do more than this — they lose their lath-hke cha- 

 racter, and help to form the rich diploe of this region, most of which is contributed by 

 the sphenoido-frontals. Generally in birds these ethmoidal roof-bones may be distin- 

 guished more easily than most of the elements of the upper surface of the head, if we 

 except the lacrymals ; and in several Struthious birds, Galline birds, and Rails, they 

 continue pretty distinct throughout life, whilst in a great proportion of species traces of 

 the sutural lines are persistent. This character, combined with their thin, fibrous, 

 elastic condition, makes them very traceable. But this is not always the case ; for in 

 birds with a dense, close skull-wall, e. g. Parrots, Hornbills, Toucans, and Balaeniceps, 

 — and even with a cellular skull, as in the Podargus, — the traces of composite structure 

 in these regions are most of them entirely obliterated. In most typical birds, the nasal 

 either overlaps, pushes aside, or passes under the great frontal (its successor), becoming 

 more or less anchylosed with it : anteriorly it splits or bifurcates, the upper process 

 passing along the inferior and outer margin of the nasal process of the pre-maxillary, 

 whilst the lower process passes downwards and forwards to join the palatal process of 

 the maxillary and the maxillary itself. The extreme degree of coalescence which has 

 taken place in this somewhat immature skull of the Balaeniceps makes it impossible to 

 point out the boundaries of the nasals ; but some large skulls of the Common Duck 

 scarcely half a year old, in which the sutures are still very evident, and the skull of 

 the Heron will give a good idea of the relations and extent of this bone. The Adjutant 

 {Leptoptilus), moreover, even in old age shows the sutural lines in this region, in rows 

 of canals and passages, just as the facial extent of the lacrymal of Balaeniceps is shown. 

 In the latter bird, the width of the bone in front of the great cranio-facial hinge is 

 barely two inches ; in the former it is slightly above that measurement, and yet the width 

 is not eked out by the lacrymals as in Balaeniceps. The nasal processes of the pre- 

 maxillaries in the Adjutant are each half an inch wide at the hinge, the nasals being of 



