32 BILCOCK—BILL 
1175 ; and states that the Cirriped (Lepas anatifera), also so-called, 
took its name from the Bird,a kind of Gooss, and not the Bird 
from the Cirriped. 
BILCOCK, said to be a local name for the Water-RAIL. 
BILL or BEAK, in Latin Rostrum. ‘This consists of an upper, 
chiefly premaxillary and maxillary, and of a lower, or mandibular, 
half. The horny covering is to a certain extent moulded after the 
shape of the supporting bones. The soft cutaneous portion of the 
skin is frequently restricted to a thin layer between the periosteum 
and the Malpighian layer of the epiderm ; in it run numerous blood- 
vessels. and nerves, the latter occasionally penetrating the horny 
layer, and ending in tactile or sensory corpuscles. 
On the other hand, in very stout beaks, the cutaneous layer 
forms conical elongations which project into the thick horny parts, 
especially into the ends of the upper and lower bill. In the broad 
edge of the mandible of Parrots such projections are particularly 
numerous and long; when they calcify, as cutaneous structures 
are liable to do, they bear in horizontal sections a superficial 
resemblance to the germs of teeth, and have been mistaken as such 
by various anatomists (see TEETH). 
The horny sheath, or rhamphotheca, is produced by the 
outer layers of the Malpighian cells, and resembles in structure 
other horny parts, as CLAWS, nails, and spurs. Sometimes, as 
in the Anseres, the greater portion of the outer sheath of the bill is 
soft, and only the tip of the bill is transformed into a thick horny 
“neb,” which contains numerous tactile organs. In some birds, 
especially in the diurnal Birds-of-Prey and in the Parrots, the 
greater portion of the distal end of the upper beak is hard, while the 
basal portion is thick and soft—the so-called cere. It is generally 
very sensitive, and encloses the nostrils. Though mostly bare, 
it is in some Parrots thickly covered with feathers, and then 
approaches in structure the ordinary skin. The neighbourhood of 
the nostrils is often soft, and produces an operculum by which, in 
some cases, the external nares can apparently be closed, although 
no muscles seem to exist there. Such a soft and swollen operculum 
is a prominent feature in Pigeons, and is very large and curled in 
Rhinochetus (KAcu). In the Petrels each operculum forms a more 
or less complete tube, which may or may not fuse with its counter- 
part in the middle line, and thus produce an apparently single tube 
with a longitudinal vertical septum, whence the name “ 'Tubinares.” 
A leathery operculum or valve also occurs in Plovers, in 
Podargus, many Passeres (especially shewn in Meliphagidz), and 
in the Humming-birds, in the last being covered with feathers. In 
Caprimulgus each nostril is produced into a short, narrow, and 
quite soft tube. 
Another differentiating feature in connexion with the nostrils 
