MR. W. K. PARKER ON THE OSTEOLOGY OF BALjENICEPS 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 most so. 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 

 thelacrymal 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. Tlie 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 Balseniceps. 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 Balceniceps 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 PreB-maxilla. 



In the Balaeniceps 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 



