302 MR. W. K. PARKER ON THE OSTEOLOGY OF BALZNICEPS REX. 
position anteriorly ; posteriorly it lies below and within the third moiety, the ‘ quadrato- 
jugal ’—this latter element articulating with the external part of the base of the os 
quadratum. ‘This zygomatic arch is nearly two inches long, its vertical breadth six 
lines or thereabouts (its middle being rather less), whilst its average thickness is three 
lines. 
The upper and lower margins of this compound zygoma are rounded, but slightly 
thinned off and keeled, the former mostso. ‘The internal surface is smooth and convex, 
the external convexo-concave, the thickest and most convex part being near the lower 
margin, at the posterior third. The anterior end of the external part is articulated with 
the lacrymal and the posterior angle of the maxillary, which lies outside the base of the 
lacrymal above; it then sends a process into the substance of the maxillary, whilst 
below it is overlapped by it. There is evidently some articular cartilage here in the fresh 
state, as this hinge is rather freely moveable, notwithstanding the complete coalescence 
of the interior part of the zygoma with the upper jaw or maxilla. The extreme elasticity 
of the zygomatic plate of the maxillary allows of this movement ; and we may remark 
that this anterior zygomatic joint has the compound character of arthrodia, gomphosis, 
dentate suture, and anchylosis. The upper margin of the bone is at first convex, and 
then concave, and convex again behind ; and here, at the posterior fifth, there is a rough 
notched tubercle. The margin then suddenly falls, is crescentic in shape, and at the 
hinder tip of the crescent sends inwards a strong subconical process a quarter of an inch 
long, and at right angles to the main bone. The lower margin of the bone is nearly 
parallel with the upper, but is more internal, and is very convex as it lowers itself to 
become nearly parallel with the large crescentic notch above. The posterior internal 
process of the zygoma, best developed in Herons of any group, fits into a deep concavity 
of the os quadratum. The compound zygomatic bone is one of the rich and unique parts 
of the structure of Baleniceps. No other bird has anything comparable with it. The 
strongest of all birds’ skulls is that of the Helmet Hornbill (Buceros galeatus), where the 
surface of the cranium is as deeply pitted as in the Crocodile; but here the zygoma is 
only one-third the size of that in Baleniceps rex. The zygoma in the Boat-bill and the 
Herons is more like an ossified tendon than anything else; and in the Adjutant it is 
relatively no stronger. 
Development of Pre-mazilla. 
In the Baleniceps all trace of suture between even the nasal processes of the pre- 
maxillaries is entirely lost, as much as in the Parrots and Hornbills ; faint traces of this 
mesial suture may be seen in old Adjutants and-Herons; whilst in a great number of 
birds it is distinct throughout life nearly down to the main body of the bone. In both 
the Chick and the young Pigeon, coalescence takes place rapidly between the lateral pieces 
up to the anterior end of the nasal passages. On the eleventh day of incubation the 
pre-maxillaries of the Chick are quite distinct, and a considerable oval space exists at 
