THE ANATOMY OF BIRDS. — NEUROLOGY. 
191 
horizontal canals are divided rapid movements of the head from side to side, in a liorizontal 
plane, take place, along with oscillation of the eyeballs, and the animal tends to spin round on 
a vertical axis. When the postei-ior 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 hands of birds being 
hidden in the feathers which envelop the wliole 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 qualities 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 
sensations 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 
part, of the t(mgue, 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 realized 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 
aud 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 woodcock, true snipe, and 
sandpipers, the bill is a very delicate nervous probe. The 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 betw^een 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 of birds and other animals are commonly reckoned as five — a number which 
may be defensively increased — as by a sixth, the muscular sense, which gives consciousness 
of strain or resistance, apart fi'om purely tactile impressions ; and perhaps a seventh, the 
faculty of equilibration, which has a physical mechanism of its own, at least as distinct and 
complete as that of hearing. The ordinary "five senses" are curiously graded. Taction con- 
