464 MANUAL OF ZOOLOGY. 



birds — the hallux is wholly wanting, or is rudimentary. In the 

 Emeu, Cassowary, Bustards, and other genera, the hallux is 

 invariably absent, and the foot is three-toed. In the Ostrich 

 both the hallux and the next toe (" index ") are wanting, and 

 che foot consists simply of two toes, these being the outer .toe 

 ind the one next to it. The toes are mechanically flexed 

 during the sleep of the Bird, in virtue of an arrangement by 

 which, whilst all the flexor tendon^ pass behind the heel, one 

 of them nms in front of the knee. As the muscles, therefore, 

 are relaxed during sleep, and the weight of the body tends to 

 flex the knee, the tendon of this flexor is thereby put on the 

 stretch, and the toes are again bent involuntarily. 



The digestive system of birds comprises the beak, tongue, 

 gullet, stomach, intestines, and cloaca. Teeth are invariably 

 wanting in birds, and the jaws are encased in horn, constitut- 

 ing the bill. The form of the bill varies enormoiisly in differ- 

 ent 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, 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 dilatable. 

 In the carnivorous, or Raptorial, and in the granivorous birds, 

 the gullet (fig. 183, d), 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" (c), 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 cesophagus, after leaving the crop, shortly opens 



