216 



GENERAL ORNITHOLOGY. 



that is, excited by the presence of food, — having work to do making it work, so to speak. Its 

 innervation is chiefly by the pueuniogastric and sympathetic nerves; and digestion is the most 

 purely vegetative function, dealing with the raw materials of nutrition and consequently of the 

 growth and repair of the whole body. The active fiictors in this transaction are several spe- 

 cies or varieties of small creatures, caUed Enteramoebm; they are all derived by descent with 

 modification from the hypoblastic cells of the early embryo. Those of the canal itself form 

 all the mucous epithelium of that structure, with its various secretory crypts, follicles, and villi ; 

 similar creatures, perhaps of different genera, form the lining of the salivary, hepatic, and pan- 

 creatic glands. Blood-vessels, in intimate connection with the digestive organs, form that 

 special venous arrangement by which the blood coming from that part of the intestinal tract 

 where chyle is made is collected in a^^ortaZ system and sent through the liver, — in the embryo 

 a sort of "great dismal swamp" which interrupts the ordinary current. The tube within the 

 tube is fixed not only at its ends, but by various membranous connections, among them the 

 mesenteries. We will notice the several departments of the alimentary canal, and its annexes ; 

 reference should be made to the colored frontispiece, and to fig. 101, where most parts of the 

 digestive system are shown. 



The Mouth and Tongue. — The most anterior of the special cavities in which the tube 

 is divided, and the " manual " organ it contains. The mouth in general corresponds to the 

 a shape of the jaws, already sufficiently noted (pp. 105, 168). The 



anterior part is much hardened, like the beak ; in fact, this hard- 

 ness of the buccal cavity, and the absence, or very slight distinc- 

 tion, of a " soft palate," are among the peculiarities of a bird's 

 mouth. There is consequently little distinction, if any, between 

 mouth proper and fauces, or pharynx, which is the posterior part, 

 leading directly into the gullet. Besides 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 arc the remains of the 

 first post-oral visceral cleft of the early embryo. 3. The glottis (fig. 

 101, ^, c), a slit at the base of the tongue, the opening of the wind- 

 pipe, 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, coiTesponding to the parotid, submaxillary, and 

 sublingual glands of mammals, vary extremely in their develop- 

 ment. In M'oodpeckers, for example, and some Raptores, elaborate 

 special salivary glands occur, having a glomerate structure, and 

 a special " stenonine " duct. In many other birds, similarly com- 

 pound but less elaborate submaxillary glands pour their secretion 

 into the mouth by a series of pores. In most birds, however, 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 struc- 

 ture ; a great pouch opening beneath the tongue, susceptible of distension during those amatory 

 antics termed the " showing-off " of the creature. It is in fact an air-sac, but not of the kind 

 already considered (p. 200), having no connection with the respiratory system. The narial, 

 eustachian and glottidean apertures are commonly defended by retrorse papillfe ; and other such 



Fig 102. — Gular pouch of 

 bustard ; copied by Shufeldt 

 from Garrod. a, tongue; h, 

 the pouch, opening under a, 

 hanging in front of c, the tra- 

 chea, behind which is the 

 oesophagus, d, with its crop, e. 



