32 BILCOCK—BILL 



1175 ; and states that the Cirriped {Lepas anatifera), also so-called, 

 took its name from the Bird, a kind of GooSE, and not the Bird 

 from the Cirriped. 



BILCOCK, said to be a local name for the Water-RAIL. 



BILL or BEAK, in Latin Eostrum. 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 sixperficial 

 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 Cl-A-WS, 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 

 Khinochetus (Kagu). 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 Meliphagidae), 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 



