SEC. IV ANATOMY OF BIRDS 283 



lymph has a wonderful office — that of equilibration, enabling the 

 animal to preserve its equilibrium. The labyrinth and its contained 

 fluid may be likened to the glass tubes filled with water and a 

 bubble of air, by a combination of which a surveyor, for example, 

 is enabled to adjust his theodolite true to the horizontal. Some- 

 how a bird knows how the fluid stands in the self-registering level- 

 ling-tubes, and adjusts itself accordingly. Observations made on 

 pigeons show that " when the membranous canals are divided, very 

 remarkable disturbances of equilibrium ensue, which very in char- 

 acter according to the seat of the lesion. When the horizontal 

 canals are divided rapid movements of the head from side to 

 side, in a horizontal plane, ts^ke 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. Combined 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 

 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 qualities of substances 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 painfully 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 instrument 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 



