210 
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 pneumogastric 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 factors in this transaction are several spe- 
cies or varieties of small creatures, called Enteramoebes; 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 diflferent 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 portal 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 
shape of the jaws, already sufficiently noted (pp. 100, 162). 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 pai-t, 
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 are the remains of the 
first post-oral visceral cleft of the early embryo. 3. The glottis (fig. 
101, 3, 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, corresponding to the parotid, submaxillary, and 
sublingual glands of mammals, vary extremely in their develop- 
ment. In woodpeckers, 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 " shovdng-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 papillae ; 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, beliind which is the 
oesopliagus, d, with its crop, e. 
