SEC. IV ANATOMY OF BIRDS 313 



The tongue is moved by some intrinsic muscles, as vrell as by those 

 extrinsic ones by which it is connected to the skull, jaw, and wind- 

 pipe (Fig. 101, 1 and «). 



The (Esophagus. — After comminution, if any, by the beak, and 

 insalivation in the mouth, food passes directly through the pharynx 

 into the msophagus or gullet, — a musculomembranous tube connect- 

 ing mouth with stomach (Fig. 101, 1, g, h, i). This is composed 

 (besides its mucous membrane) of circularly disposed constrictor fibres, 

 and longitudinal contractm- fibres, of Myamceba, of the pale, smooth 

 species (M. Icevis). It has generally a pretty straight course, but 

 may be diverted to one side or the other ; and, in particular, is 

 subject to various dilatations and contractions, permanent or tem- 

 porary, aside from the mere distension caused by the passage of 

 food. When the floor of the mouth is wide and loose, the gullet 

 partakes of the same character above ; the extreme case is afforded 

 by the pelicans, especially Pelecanus fuscus. But the gullet of many 

 small birds, as various genera of FringillidcB and Corvidce, is much 

 more distensible than is commonly supposed, and may be found 

 crammed with seeds which there find resting-place for some time. 

 The fish-eating birds, as herons, cormorants, loons, and others, have 

 also capacious gullets. The Australian bustard, Eupodotis australis, 

 has an oesophagus capable of such extraordinary distension that it 

 hangs down in front of the breast when inflated with air, as it is in 

 . the amatory display in which that species is wont to indulge. 

 Aside from mere distensibility of transient character, the oesophagus 

 of many birds becomes modified anatomically into a special pouch, 

 — the crop or craw, ingluvies, where the food is detained to be macer- 

 ated in a special secretion before passing on to the true stomach. 

 Such definite crops occur in birds of prey, which gorge such masses 

 of food in their irregular voracious banquets that it cannot all be 

 received into the stomach at once ; and likewise throughout the 

 orders of Columbine and Gallinaceous birds, which habitually feed 

 upon seeds and other fruits so hard that they are advantageously 

 macerated as a preliminary to true digestion. The common fowl 

 furnishes a good illustration of a large, definite, single and median 

 crop ; in pigeons it is a pair of lateral dilatations. In these latter 

 birds, when they are rearing their young, the secretion of the inglu- 

 vies, always copious, becomes still more so, and of a milky character 

 in consequence of the activity of the altered mucous surface ; it is 

 regurgitated into the mouths of the young along with the macer- 

 ated grains. "This phenomenon is the nearest approach in the 

 class of Birds to the characteristic mammary function of a higher 

 class ; and the analogy of the ' pigeon's milk ' to the lacteal secre- 

 tion of the Mammalia has not escaped popular notice." Various 

 other bifds also feed their young by regurgitation of elaborated 



