276 MR. W. K. PARKER ON THE OSTEOLOGY OF BALiENICEPS REX. 



In Balseniceps, as in the great Maccaws, the orbital margin of the frontalis higher (in 

 the former |^th of an inch) than the mesial part of the bone ; and this marginal elevation 

 in both kinds subsides gently into the slightly concave upper interorbital surface of the 

 frontals. In the Maccaws and in the Balaeniceps, the highest part of the cranium is 

 between the post-frontal processes ; and in the latter the shape of the cranial cavity is 

 in some degree marked out on the external table of the frontal and parietal bones. 

 The orbital margin of the frontal (or, as Professor Goodsir calls it, the sphenoido- 

 frontal) in Balaeniceps is, as is usual in this class, more or less notched or perforated 

 by vessels. In the Boat-bill and in the Heron, the large eye-ball has elevated the 

 orbital margin of the sphenoido-frontal ; but this takes place most in the latter, in which 

 bird the concavity between these margins is unusually deep. 



In the rough, unevenly convex cranium of the Adjutant, the orbital margin is nearly 

 half an inch below the mid-line of the frontal. 



In Balaeniceps, a gentle ridge of bone, arising from the posterior edge of the post- 

 frontal process (figs. 1, 3, 6,pf) passes upwards and backwards to the distance of about 

 two-fifths of an inch from the mesial line of the skull in the parietal region, and to one- 

 third of an inch in front of the epiotic eminence. This gently curved ridge is the 

 anterior boundary of the temporal fossa (Pi. LXV. figs. 1 & 3, tf), which is subtrian- 

 gular in shape, and has for its posterior margin a line, nearly at right angles to its 

 anterior boundary, which line runs outwards, downwards, and backwards, losing itself 

 in the ridged crest of the upper mastoid eminence. The inferior margin of the tem- 

 poral fossa is incomplete in front, there being a large semi-oval space between the 

 post-frontal process and the articular surface of the base of the squamosal for the 

 external condyle of the head of the os quadratum. Behind this external quadrato- 

 squamosal facet a rough ridge of bone runs horizontally across, losing itself in the 

 fossa between the upper mastoid eminence and the ' par-occipital' ala ; this ridge 

 defines the temporal fossa below and behind. 



These fossae are ten lines apart in Balaeniceps ; in the highly arched head of the 

 Adjutant they do not meet by two inches ; the distance of these fossae in Buceros bicornis 

 is one inch and four lines, in the Maccaw one inch and six lines ; and in the Pelican 

 they do not approximate more than in the Maccaws. 



But in many birds, e. g. the Heron, Boat-bill, Podargus, Diver (Colymbus), and the 

 larger Grebes {Podiceps), the temporal fossae are only separated by a sharp interparietal 

 crest, whilst their anterior and posterior boundaries are almost parallel. This is like 

 what obtains in many other vertebrata, the extreme conditions of this sagittal ridge 

 being found in such fishes as the Ephippus, Pagellus, and Platax arthriticus ; in the Cha- 

 meleon amongst the reptiles ; and, in the mammals, in such skulls as those of the Tiger, 

 Hyena, and certain Bats, e. g. Molossus obscurus. 



The post-frontal process of the Balaeniceps is strong, and descends downwards, and 

 also slightly outwards and forwards, its length being eight lines. The end of this 



