AVES. 



311 



Organ of Tasle. The gustatory sense is very 

 imperfectly enjoyed in birds, which, having no 

 manducatory organs, swallow the food almost 

 as soon as seized. The tongue is organized 

 chiefly to serve as a prehensile instrument, and 

 its principal modifications will be treated of 

 under the head of the Digestive Organs. It is 

 generally sheathed at the anterior part with 

 horn (hjjig. 152), and is destitute of papillae 

 except at its base (o, fig. 152) near the aper- 

 ture of the larynx ; these papillae are not, how- 

 ever, supplied by a true gustatory nerve, but by 

 filaments of the glossopharyngeal. No branch 

 of the fifth pair goes to the tongue. 



The tongue is proportionally largest and 

 most fleshy in the Parrot tribe, and the food 

 is detained in the mouth longer in these than 

 in other birds. It is triturated and commi- 

 nuted by the mandibles certainly, and turned 

 about by the tongue, which here seems to ex- 

 ercise a gustatory faculty, since indigestible 

 parts, as the coat of kernels, &c. are rejected. 

 In the Lories the extremity of the tongue is 

 provided with numerous long and delicate pa- 

 pillae or filaments projecting forwards. 



Organs of Touch. With respect to the tactile 

 instruments, but few observations can be made 

 in the class of Birds. The anterior extremities 

 have their digital extremities undivided and 

 entirely unfitted for the exercise of this sense, 

 and the posterior extremities are but little better 

 organized for the purpose. The integument 

 covering the toes is very sparingly supplied 

 with nerves, and is of a texture scarcely fitted 

 for ascertaining the superficial qualities of 

 bodies. However, the villi on the under sur- 

 face of the toes are observed to be remarkably 

 long in the Capercailzie (Tetrao urogallus), 

 but this is probably for the purpose of enabling 

 them to grasp with more security the frosted 

 branches of the Norwegian pine-trees. The 

 Parrots seem to use their feet more like instru- 

 ments of touch, but in them the action may 

 be merely prehensile. 



The only organ of touch respecting which 

 there can be no doubt is the bill. Even where 

 this is covered with a hard sheath of horn, some 

 filaments of the fifth pair (c,fig. 150) may be 

 traced terminating in small papillae ; but in the 

 Lamelli-rostral water-birds the bill is covered 

 by a softer substance, and is plentifully supplied 

 by branches of the fifth pair of nerves. (See 

 Nerves.) In the Woodcocks and Snipes the 

 long bill is so organized that it is used as a 

 probe in marshes and soft ground to feel for 

 the small worms and slugs that constitute their 

 food. 



The cire in the Falconida, the wattles of 

 the Wattle-birds (Philedon carunculatus and 

 Gkmcopis cinerea) and of the Cock, the ca- 

 runcles of the King-Vulture and Turkey, may 

 also be regarded in some degree as organs of 

 touch. 



Organs of Digestion. The digestive function 

 in birds is necessarily extremely powerful and 

 rapid in order to supply the waste occasioned 

 by their extensive, frequent, and energetic mo- 

 tions, and in accordance with the rapidity of 



their circulation and their high state of irrita- 

 bility. * 



The parts to be considered with reference to 

 this function are the rostrum or beak, the 

 tongue, the oesophagus, the stomach which is 

 always divided into a glandular and muscular 

 portion, the intestines, and the cloaca. 



The glandular organs of the digestive system 

 are the salivary glands, the proventricular fol- 

 licles, the liver, pancreas, and spleen. 



The beak consists of the maxillary and inter- 

 maxillary bones, which in place of teeth are 

 provided with a sheath of horny fibrous mate- 

 rial, exactly similar to that of which the claws 

 are composed: this sheath is moulded to the 

 shape of the osseous mandibles, being formed by 

 a soft vascular substance covering these parts, and 

 its margins are frequently provided with horny 

 processes or laminae secreted by distinct pulps, 

 and analogous in this respect to the whalebone 

 lamina; of the Whale: M. Geoffrey St. Hilaire 

 has described a structure in the bill of birds 

 which presents a closer approach to a dentary 

 system. In a foetus of a Perroquet nearly ready 

 for hatching, he found that the margins of the 

 bill were beset with tubercles arranged in a re- 

 gular order and having all the exterior appear- 

 ances of teeth : these tubercles were not, indeed, 

 implanted in the jaw-bones, but formed part 

 and parcel of the exterior sheath of the bill. 

 Under each tubercle, however, there was a ge- 

 latinous pulp, analogous to the pulps which 

 secrete teeth, but resting on the edge of the 

 maxillary bones, and every pulp was supplied 

 by vessels and nerves traversing a canal in the 

 substance of the bone. These tubercles form 

 the first margins of the mandibles, and their 

 remains are indicated by canals in the horny 

 sheath subsequently formed, which contain a 

 softer material, and which commence from 

 small foramina in the margin of the bone. 



The different degrees of hardness and varieties 

 of form of the beak exercise, Cuvier observes,f 

 as much influence upon the nature of birds as 

 the number and figure of the teeth do upon 

 that of Mammals. 



The beak is hardest in those birds which 

 tear their prey, as in Eagles and Falcons ; or 

 in those which bruise hard seeds and fruits, as 

 Parrots and Gros-beaks; or in those which pierce 

 the bark of trees, as Woodpeckers, in the larger 

 species of which the beak absolutely acquires 

 the density of ivory. 



The hardness of the covering of the beak 

 gradually diminishes in those birds which take 

 less solid nourishment, or which swallow their 

 food entire; and it changes at last to a soft skin 

 in those which feed on tender substances, or 

 which have occasion to probe for their food in 

 muddy or sandy soils, or at the bottom of the 

 water, as Ducks, Snipes, Woodcocks, &,c. 



C&teris paribus, a short beak must be stronger 

 than a long one, a thick one than a thin one, a 

 solid one than one which is flexible ; but the 



* The Cormorant readily devours six or eight 

 pounds of fish daily. 



t Anatomie Compuree, torn. ii. p. 192. 



