584 MANUAL OF ZOOLOGY. 



processes of two sizes; and in the Odontornithes of the Cre- 

 taceous period the jaws are furnished with true teeth implanted 

 in distinct sockets. The form of the bill varies enormously 

 in different birds, and it is employed for holding and tearing 

 the prey, for prehensile purposes, for climbing, and in some 

 birds as an organ of touch. In these last-mentioned cases the 

 bill is more or less soft, and is supplied with filaments of the 

 fifth nerve. In many birds, too, in which the bill is not soft, 

 the base of the upper mandible is surrounded by a circle of 

 naked skin, constituting what is called the " cere," and this, 

 no doubt, serves also as a tactile organ. 



The tongue of birds can hardly be looked upon as an organ 

 of taste, since it is generally cased in horn like the mandibles. 

 It is, in fact, principally employed as an organ of prehension ; 

 but in some cases as in the Parrots it is soft and fleshy, and 

 then, doubtless, is to some extent connected with the sense 

 of taste. It is essentially composed of a prolongation of the 

 hyoid bone (the glosso-hyal), which is sheathed in horn, and 

 is variously serrated or fringed. 



Salivary glands are invariably present, but they are rarely 

 of large size (they are very large in the Woodpeckers and 

 Swifts), and they have often a very simple structure. 



In accordance with the structure of the neck, the gullet in 

 birds is usually of great length, and it is generally very dilat- 

 able. In the carnivorous, or Raptorial, and in the granivorous 

 birds, the gullet (fig. 326, o] is dilated into a pouch, which is 

 situated at the lower part of the neck, just in front of the 

 merry - thought. This is what is known as the " crop " or 

 "ingluvies" (<:), and it may be either a mere dilatation of the 

 tube of the gullet, or it may be a single or double pouch. 

 The food is detained in the crop for a longer or shorter time, 

 according to its nature, before it is subjected to the action of 

 the proper digestive organs. The oesophagus, after leaving 

 the crop, shortly opens into a second cavity, which is known 

 as the " proventriculus " or " ventriculus succenturiatus " (/). 

 This is the true digestive cavity, and its mucous membrane 

 is richly supplied with gastric follicles which secrete the gastric 

 juice. The proventriculus, however, corresponds, not with the 

 whole stomach of the Mammals, but only with its cardiac, 

 portion \ and it opens into a second muscular cavity, which 

 corresponds to the pyloric division of the Mammalian stomach. 

 The gizzard (g) is situated below the liver, and forms in all 

 birds an elongated sac, having two apertures above, of which 

 one conducts into the duodenum, or commencement of the 

 small intestine, whilst the other communicates with the pro- 



