THE ANATOMY OF BIEDS. — NEUROLOGY. 197 



horizontal canals are divided rapid movements of the head from side to side, in a horizontal 

 plane, take place, along with oscillation of the eyeballs, and the animal tends to spin round on 

 a vertical axis. When the posterior or inferior vertical canals are divided, the head is moved 

 rapidly backwards and forwards, and the animal tends to execute a backward somersault, head 

 over heels. When the superior vertical canals are divided, the head is moved rapidly forwards 

 and backwards, and the animal tends to execute a forward somersault, heels over head. Com- 

 bined section of the various canals causes the most bizarre contortions of the head and body." 

 (Ferrier, Funct. of the Brain, 1876, p. 57-) Injury of the canals does not cause loss of hearing, 

 nor does loss of equilibrium follow destruction of the cochlea. Two diverse though intimately 

 connected functions are thus presided over by the acoustic nerve, — audition and equilibration. 



Senses of Taste and Touch : Gustation and Taction. — The liands of birds being 

 hidden in the feathers which envelop the whole body — their feet and lips, and usually much 

 if not all of the tongue, being sheathed in horn, these faculties would appear to be enjoyed in but 

 small degree. While it is difficult to judge how much appreciation of the sapid quahties of sub- 

 stances birds may be capable of, we must not be hasty in supposing their sense of taste to be 

 much abrogated. One who has had the toothache, or teeth " set on edge" by acids, or pain- 

 fully affected by hot or cold drinks, may judge how sensitive to impressions an extremely dense 

 tissue can be. Persons of defective hearing may be assisted to a kind of audition by an instru- 

 ment applied to the teeth ; and it is not easy to define the ways in which sensory functions may 

 be vicariously performed or replaced. Birds are circumspect and discriminative, even dainty, in 

 their choice of food, in which they are doubtless guided to some extent by the gustatory 

 «;ensations they experience. As, however, only some human beings make these an end instead 

 of a natural and proper means to an end, the selection of food by birds may be chiefly upon 

 intuitions of what is wholesome. Such purely gustatory sense as they possess is presided over 

 by the branches of the glosso-pharyngeal nerve which go to the back part of the tongue and 

 mouth. Though the chorda tympani nerve exists, there is no lingual (gustatory) branch of the 

 third division of the fifth cranial nerve. Yet the latter, which goes in mammals to the anterior 

 ])art of the tongue, is less effectually gustatory than the glosso-pharyngeal ; as we know by the 

 fact that the sensation of taste is not completely experienced until the sapid substance passes to 

 the back of the mouth. Gustation is likewise connected with olfaction ; the full effect of 

 nauseous substances for example, being not realizeu if the nose is held. From these alternative 

 considerations, each one may estimate for himself how much birds know of sapidity ; remember- 

 ing also, how soft, thick, and fleshy are the tongue and associate parts in some birds, as parrots 

 and ducks, in comparison with birds whose mouths are quite horny. 



The beak is doubtless the principal tactile instrument ; nor does its hardness in most birds 

 preclude great sensitiveness ; as witness the case of the teeth, above instanced. Sensation is 

 here governed by the branches of the fifth nerve. In some birds, in which also the terminal 

 filaments of this nerve are largest and most numerous, the bill acquires exquisite sensibility. 

 Such is its state in the snipe family, in most members of which, as the wtiodcock, true snipe, and 

 sandpipers, the bill is a very delicate nervous probe. Tlie Apteryx also feels in the mud for 

 its food, enjoying moreover the unusual privilege of having its nose at the end of its long 

 exploration. Ducks dabble in the water to sift out proper food between the " strainers " with 

 which the sides of their beaks are provided ; and the ends of the maxillary and mandibular bones 

 themselves are full of holes, indicating the abundance of the nervous supply (fig. 63). 



The senses oi birds and other animals are commonly reckoned as five — a number whicli 

 may be defensively increased — as by a sixth, the muscular sense, which gives consciousness 

 of strain or resistance, apart from purely tactile impressions ; and perhaps a seventh, the 

 faculty of equilibration, which has a ])1iysical mechanism of its own, at least as distinct and 

 complete as that of hearing. The ordinary "five senses" are curiously graded. Taction cou- 



