398 ORGANS OF DIGESTION. 



in the strutheous birds, arrow-shaped in the gallinacea, long, 

 broad, and covered with large recurved spines in the swans, 

 short, round and highly flexible in the cockatoos and parrots; 

 but the body and cornua of the os hyoides are always com- 

 paratively long, slender, and flexible in this class. 



As the food of birds is not masticated nor retained in the 

 mouth, the salivary glands are smaller than in quadrupeds, 

 more simple in structure, and commonly disposed in four 

 pairs, one situate under the sides of the tongue, another at 

 the junction of the rami of the lower jaw, another close to 

 the base of the cornua of the os hyoides, and another at the 

 angles of the mouth. The mouth is provided with numerous 

 muciparous glands, and the salivary glands are most deve- 

 loped in gallinaceous and frugivorous birds, as in herbivorous 

 quadrupeds. The closed ends of the tubuli salivarii are more 

 or less dilated, as in other classes of animals, and the isolated 

 vertical tubuli composing the first or sublingual pair open 

 separately into the mouth by a row of pores. The second 

 pair open by several ducts under the fore part of the tongue: 

 the third, or submaxillary pair, open behind the second, 

 sometimes by elongated ducts ; and the fourth pair open 

 within the angles of the mouth. The uvula, velum, and epi- 

 glottis, not being yet developed, the posterior nares and the 

 larynx are but little protected, and the oesophagus, with a 

 simple entrance, is here wide, muscular, and of great length, 

 corresponding with the great length of the neck in birds. 



As in other classes of animals, the whole alimentary canal 

 of birds varies much in its length and capacity, and in the 

 form and development of its cavities, according to the nature 

 of the food, being long and capacious, with large glandular 

 organs and muscular parietes, in the various phytophagous 

 tribes, and with the reverse of these characters in those which 

 feed more exclusively on animal food. The long, wide, mus- 

 cular oesophagus, with a smooth mucous coat, and thin epi- 

 dermic lining, passes down behind and a little to the right 

 side of the trachea, as seen in the annexed figure of the vis- 

 cera of the gallus domesticus, (Fig. 128. a,} and about the 

 middle of its course, a little above the two anchylosed clavi- 

 cles, it presents, in gallinaceous, raptorial, and many other birds, 

 an enlargement, an ingluvies or crop, (128. b.) varying in form 

 and structure according to the difference of the food, and 



