FUNCTIONS OF THE SENSORY GANGLIA. 659 



causes the animal to make continued forward "somersets;" whilst section of 

 the posterior vertical canal occasions continued backward "somersets." The 

 movements cease when the animal is in repose ; and they recommence when 

 it begins to move, increasing in violence as its motion is more rapid. These 

 curious results are supposed by M. Flourens to indicate, that the nerve sup- 

 plying the semicircular canals does not minister to the sense of hearing, but 

 to the direction of the movements of the animal ; whilst M. Cyon 1 refers 

 them to the circumstance that in order that an animal should preserve its 

 equilibrium, it should have a correct idea of the position of its own head, 

 and that the semicircular canals supply this information in consequence of 

 each canal having a definite relation to space. But they are more rationally 

 explained upon the supposition, that the normal functions of the semicircular 

 canals is to indicate to the animal the direction of sounds, and that its move- 

 ments are partly determined by these ; so that a destruction of one or other 

 of them will produce an irregularity of movement (resulting, as it would 

 seem, from a sort of giddiness on the part of the animal), just as when one 

 of the eyes of a bird is covered or destroyed, as in the experiments previ- 

 ously cited. Goltz, 2 however, has recently maintained that the position 

 of the head is judged of by the animal from the pressure exerted by the 

 endolymph on one side or the other of the semicircular canals ; and that 

 when the endolymph has escaped by section of the canals, neither the eye 

 nor the muscular sense can supply the a deficiency the movements of the 

 body are on this view secondary, and are due to the inability of the animal 

 to judge of its relation to surrounding objects from the position of its head ; 

 on the other hand, according to Cyon, 3 a definite perception of the position 

 of the head is necessary to the maintenance of equilibrium ; and this per- 

 ception has its origin in the semicircular canals, each canal having a cer- 

 tain determinate relation to certain grades of position. The derangement 

 of motion consequent upon division of the semicircular canals, Cyon classi- 

 fies under three heads: 1. Derangements of equilibrium, as a direct result 

 of the injury. 2. Violent movements, resulting from the irritation conse- 

 quent on the abnormal sense of hearing induced thereby. 3. Consecutive 

 symptoms, occurring some days after the operation, from the resulting in- 

 flammation of the cerebellum. 



527. The numerous experiments which have been made for the purpose of 

 determining the functions of the Thalami Optici and Corpora Striata, have 

 not yielded any very satisfactory results; and this on account of the impos- 

 sibility of completely isolating them in such a manner as to limit the opera- 

 tion (whether this be section, removal, or irritation) to them alone. Thus 

 it is impossible to remove them, either separately or conjointly, without first 

 removing 'the Cerebral Hemispheres ; and the Thalami cannot be entirely 

 removed, without dividing the stratum of fibres which traverse their deeper 

 portion in their passage to the Corpora Striata. The Thalami Optici have 

 not that relation to the visual sense which their designation would imply; 

 for (according to the affirmation of Longet), they may be completely de- 

 stroyed in Mammals and Birds, without destruction of sight or loss of the 

 activity of the pupil. And irritation of one or both of them produces no 

 contraction of the pupil. It seems probable, therefore, that the loss of 

 sight with dilatation and immobility of the pupil, which is frequently ob- 

 served in cases of apoplectic effusions into the substance of the Thalami, is 

 really due to the compression of the Optic nerves which lie beneath them. 

 These bodies appear, however, to possess a very decided influence on the 



1 Pfliiger's Archiv, Bd. viii, p. 325. 2 Ibid., Bd. iii, 1870, p. 172. 



3 See silso abstract, Knapp's Archives of Ophth. and Otol., 1874, p. 137. 



