.SEC. IV 



ANA7VMY OF BIRDS 



3" 



are among the peculiarities of a bird's moutli. There is donsequently 

 little distinction, if any, between mouth proper and fauces, (ys: pharynx, 

 which is the posterior part, leading directly into the gullet. Be- 

 sides this communication, the mouth receives the terminations of 

 four special cavities. 1. The posterior nares, on the roof of the 

 mouth posteriorly, generally a median slit leading into the nasal 

 chambers. 2. The generally single and median and more posterior 

 opening of the Eustachian tubes, which lead 

 into the tympanum, and are the remains of 

 the first postoral visceral cleft of the early 

 embryo. 3. The glottis (Fig. 101, \ c), a 

 slit at the base of the tongue, the opening 

 of the windpipe, and so of the whole 

 respiratory system, which is defended by 

 a rudimentary trap-door, the epiglottis, if 

 any. 4. One or several pairs of orifices, 

 the openings of the ducts of the salivary 

 glands. These structures, corresponding 

 to the parotid, submaxillary, and sublingual 

 glands of mammals, vary extremely in 

 their development. In woodpeckers, for 

 example, and some Eaptores, elaborate 

 special salivary glands occur, having a 

 glomerate structure and a special duct of 

 Stenson. In many other birds, similarly 

 compound but less elaborate submaxillary 

 glands pour their secretion into the mouth 

 by a series of pores. In most birds, how- 

 ever, the salivary glands are small, simple, 

 and less distinct from various other sets of 

 mucous crypts which open into the mouth. 

 In the great bustard {Otis tarda; Fig. 102) 

 there is a singular buccal structure : a great from Garroci. ' a, tongue ; b, the 



. ° , , ^ o pouch, opening under a, hanging 



pouch Openmg beneath the tongue, SUSCep- in front of c, the trachea, behind 



tible of distension during those amatory wuch^s tte <.sophagus, d, with 

 antics termed the " showing - off " of 



the creature. It is in fact an air-sac, but not of the kind already 

 considered (p. 296), having no connection with the respiratory 

 system. The narial. Eustachian, and glottidean apertures are com- 

 monly defended by retrorse papillae ; and other such processes of 

 mucous membrane, knobbed or acute, may Occur elsewhere in lines 

 and patches. The roof of the mouth is nearly all " hard palate," 

 as already said ; its soft floor is the raucous membrane and skin 

 between the forks of the under jaw, with muscular or other interven- 

 ing structures. The principal flooring muscle is the mylohyoid; 



Fig. 102. — Gular pouch of 

 bustard ; copied by Shufeldt 



