PICARIAN BIRDS. 9] 
Family X. Bucrrotipa. Horners. (Plate XIX.) 
These remarkable looking birds, ranging from Africa and the Indo- 
Malayan regions to the Solomon Islands, derive their name from their 
immensely developed bill, surmounted in most of the genera by a 
variously-shaped casque, which is often of large dimensions and gives 
them a singularly top-heavy appearance. In spite of their size, the bill 
and casque are not nearly so weighty as one would suppose, being 
merely a horny shell supported internally by a cellular bony tissue 
of extreme delicacy. ‘This structure may be seen in the sections of heads 
exhibited in the Case, that of Dichoceros bicornis (1190) [Pl. XIX. figs. c 
& d] illustrating the normal type; while Bucoraa abyssinicus (1188) 
and Rhinoplax vigil (1212) are peculiar, the former in having the casque 
open anteriorly, the latter in having the anterior wall solid and the 
posterior part nearly filled up with parailel bony columns. The bones 
of the skeleton are also unusually pneumatic. The edges of the 
mandibles are generally roughly serrated, and the eyelid is furnished 
witli strong lashes. The feet have broad soles, the second, third, and 
fourth toes being partially united. Though often prolonged for 
considerable distances, the flight is heavy, slow, and extremely noisy, 
the sound, which has been likened to the rushing of an express train, 
being probably caused by the air passing between the open bases of 
the quills at each beat of the wings. 
The nesting-habits of these birds are peculiar, and of extreme interest. 
After the eggs have been laid in the hollow of a tree, the female 
commences to incubate, and the male (sometimes assisted by his mate) 
closes up the entrance to the nest with a very hard clay-like substance, 
leaving only a small slit through which the female can protrude her bill 
and receive the fruits he brings her. If the male is killed, other males 
are said to take his place and provide the female with food. The object 
in closing in the female is no doubt to protect her from. the attacks of 
monkeys and other enemies. 
The female is said to remain imprisoned until the young are fully 
fledged, and in some species at least the wings and tail are shed and 
renewed during this period, the moulting of these feathers being no 
doubt a welcome relief to the bird in its cramped and stuffy cell. The 
adjacent table-case, containing the nesting-site of one of the smaller 
African Hornbills (Lophoceros melanoleucus) (1204) illustrates all these 
interesting facts. 
The numerous species are divided into two subfamilies, Bucoracine 
and Bucerotine ; the former including only two very large African 
species of Ground-Hornhills characterised by their long legs, which are 
well-adapted for walking. The Abyssinian Ground-Hornbill ( Bucorax 
[Cases 
59, 60. | 
