On the other hand, the extreme delicacy of perception of movement which some persons evince when laid upon the table-top would seem to require a more delicate apparatus than that just spoken of; and there are many facts which point to a peculiar structure in the inner ear as having connection with equilibration. If in the frog the disk back of the eye be wounded deep enough to affect the nerve of hearing, the creature falls upon one side, entirely deprived of its power of balancing itself. Perfectly similar phenomena are seen not only in the mammals operated upon by the physiologist, but also in human beings, in whom wounds of the nerve of hearing, as well as ruptures of blood-vessels in the inner ear, produce a peculiar vertigo, with staggering and loss of power which have been mistaken for apoplexy. Some years since there was under my professional care a man who had been shot in the face, the bullet passing backward toward the inner ear. In this case there was complete loss of hearing on the injured side, and a peculiar giddiness, with staggering gait similar to that which follows hæmorrhage into the inner ear. The bullet had certainly penetrated into the aural region, and the vertigo was evidently like the deafness due to an injury of the inner ear. In the inner ear of all animals are the so-called _semicircular canals_, which are provided with membranous walls, and are filled with liquid. At the end of each of these canals is an enlargement known as an _ampulla_, upon which is a delicate expansion of nerve-tissue derived from the nerve of hearing. These semicircular canals are so placed that every motion of the head must produce disturbance of the liquid contents of at least one of them, and consequently alterations of pressure on the nervous tissue in the ampulla. The structure and peculiar arrangement of these canals and their contents suggest very naturally that they have some other function than that of aiding in hearing, and that they are in some way connected with equilibration--that they are, as it were, the spirit-levels of the body, and that by the shifting of their contents impulses are constantly sent up to the lower brain to direct it in the maintenance of position. This suggestion is confirmed by the results of experiment: in the pigeon and in some mammals the canals can be readily reached and divided. Such injuries to them are followed by great disturbance of the motor function of the animal, the nature of the disturbance being chiefly dependent on the seat and character of the injury. Repeated somersaults backward or forward, bizarre contortions, spinning around worthy of a whirling dervish, loss of the power of balancing on a moving perch or board, staggering gait,--these and other similar phenomena mark the disturbance of equilibration produced by wounds of the semicircular canals.