Labyrinth and Semicircular Canals in the Human Ear. 257 



fective. To indicate fully motion in space, regard must be had 

 to six directions, viz. right," left, backwards, forwards, upwards, 

 downwards. Admitting that the membranous canals satisfy our 

 requirements as to the first four directions, how are those for the 

 last two provided for ? 



Upon this point I observe that the head cannot be moved up 

 or down without a corresponding motion of the whole or of a 

 large part of the body, for which a very considerable muscular 

 effort is necessary in order to counteract or control the effect of 

 gravity. It may very well be that such increased effort affords a 

 satisfactory measure of the motion up and down, although a 

 similar criterion as regards the horizontal motions would not be 

 sufficiently exact. 



I am inclined to think that it is at least one function of the 

 nervous filaments expanded within the membranous sac and 

 utricle to indicate the fact of motion generally, and that they 

 may aid in measuring the vertical movements of the head — their 

 operation in this respect being superseded, as regards the ho- 

 rizontal motions, by the more delicate apparatus afforded by the 

 ampullae. Any such action of the nerves of the sac and utricle 

 must, of course, be enhanced by the cretaceous otolithes attached 

 to them. 



My remarks on this branch of the subject I shall conclude by 

 pointing to the two following cases illustrative of it. 



Every one who has had opportunity to observe the development 

 of children in early infancy, must be aware that there is a time at 

 which, although the child is able to maintain its head erect for a 

 few moments, any attempt to change its position is followed by 

 a wild movement of the head, partaking of the character of that 

 described as taking place in M. Flourens's pigeons when all the 

 canals had been cut. 



The explanation of this circumstance I take to be, that although 

 the child is able to keep its head erect, and has strength to move 

 the head in different directions, yet it has not so mastered the 

 indications afforded by means of the semicircular canals as to 

 enable it to regulate the motion. 



On the other hand, it is not uncommon to meet with persons 

 of middle age, and, still more, with those advanced in life, who are 

 subject to a nervous affection, under the influence of which, 

 although ordinarily they can command the motions of the head 

 like other persons, yet occasionally, and for a brief interval, they 

 appear to lose control over them, the head moving involuntarily. 



In explication of this peculiarity, I give from M. Flourens's 

 second memoir his account of the demeanour of a rabbit, one of 

 whose canals had been cut : — 



" Dans leur plus grande violence les oscillations de la tete sont 

 Phil. Mag. S. 4. Vol. 39. No. 261. April 1870. S 



