334 STRUCTURE AND CLASSIFICATION OF BIRDS 



boundary line between trachea and bronchi ; it lies between 

 the penultimate and antepenultimate tracheal rings. 



In front of the last three tracheal rings there is no par- 

 ticular modification of the trachea. The antepenultimate ring 

 is strongly ossified in front, where it is convex downwards, 

 thus leaving a considerable membranous interval between 

 itself and the ring in front. The next ring is of the same 

 size, and also ossified in front ; the tough and elastic mem- 

 brane uniting the two can be easily stretched. The last 

 tracheal ring is much narrower, but also ossified in front ; it 

 passes into the cartilaginous pessulus. Posteriorly these 

 rings are incomplete, but are joined by a particularly tough 

 membrane. The bronchial semi-rings are delicate, and not 

 so long (from before backwards) ; they naturally diminish 

 successively in length. The above description refers to H. 

 Macqueeni, but A. undulata hardly differs. 



The bustards exhibit a phenomenon known as ' showing 

 off,' which is associated with certain anatomical peculiarities. 

 The appearance of the male bird, when indulging in this 

 display, is illustrated by a plate which accompanies Dr. 

 MUEIE'S paper * upon the subject. The neck is immensely 

 puffed out, so as actually to trail upon the ground. This 

 singular behaviour on the part of the cock bird during the 

 breeding season is not confined to the European Otis tarda ; 

 it has been observed in both Eupodotis australis and E. 

 Denhami. It is curious that, though the result to all out- 

 ward appearance is much the same, the mechanism which 

 produces the inflation of the neck differs in the two cases. 

 In Eupodotis the anterior section of the oesophagus becomes 

 dilated. In Otis there is a special pouch 2 developed between 

 the two halves of the lingual frenum, which extends for a 

 considerable way down the neck. 



The tensores patagii are fairly characteristic. No bustard 



1 P. Z. S. 1868, p. 471 ; Sir W. ELLIOT, 'Notes on the Indian Bustard,' &c., 

 P. Z. S. 1880, p. 486. See also FLOWER, P. Z. S. 1865, p. 747 ; NEWTON, Ibis, 

 1862, p. 107; MUKIE, P. Z. S. 1869, p. 140; GARROP, ibid. 1874, pp. 471, 

 673 ; FORBES, ibid. 1880, p. 477. 



2 Cf. similar pouch in duck Biziura, v. p. 458. 



