SENSORY GANGLIA. CONSENSUAL ACTIONS. 709 



i 



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 passes through their deeper portion in their passage to 

 the Corpora Striata. The evidence afforded by Pathology, too, is far from being 

 self-consistent; and this, it may be surmised, from the circumstance that the 

 effects of morbid changes (particularly of sanguineous effusions) in any part of 

 the Encephalon extend themselves to other parts than those in which the ob- 

 vious lesions are found; as is abundantly proved by the great variety of pheno- 

 mena which present themselves as the results of lesions apparently similar, and 

 the similarity of the phenomena that are frequently consequent upon lesions of very 

 different parts. 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 destroyed 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 

 observed in cases of apoplectic effusion 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 power of 

 voluntary movement ; for, although an animal maintains its balance, and can be 

 made to move onwards, after the removal of the Cerebral Hemispheres, and 

 even after the removal of the Corpora Striata, yet if either of the Thalami Optici 

 be removed, the sensibility and power of voluntary movement are destroyed on 

 the opposite side of the body, and the animal consequently falls over to that 

 side (Longet). If, instead of the entire removal of one of the Thalami, an in- 

 cision be made in it without the previous removal of the Cerebrum, the animal 

 keeps turning to one side in a circular manner (evolution du maneye) : according 

 to Longet and Lafargue, this movement is directed in the rabbit towards the op- 

 posite side ; whilst Flourens states that in the frog its direction is towards the 

 injured side ; and according to Schiff 1 the destruction of the three anterior 

 fourths of this organ in the rabbit determines this movement towards the injured 

 side, whilst that of the posterior fourth determines the movement towards the 

 opposite side. No mechanical irritation of the Thalami produces either signs 

 of pain or muscular movement ; and this fact might at first appear to negative 

 the doctrine that these organs are the ganglia of common sensation. But it 

 must be borne in mind that the production of pain by mechanical injuries is by 

 no means a universal phenomenon in the case of the nerve-trunks which min- 

 ister to sensation, the olfactive, optic, and auditory nerves being exempted ; and 

 it need occasion still less surprise, therefore, that a nervous centre should be 

 destitute of this kind of impressibility. The effects of lesions of the Corpora 

 Striata are less distinctly marked. It was affirmed by Magendie that there 

 exists in them a motor power, which excites backward movement, and that a 

 corresponding power of exciting forward movement exists in the Cerebellum; 

 and these two powers ordinarily balance each other ; but that, if either organ 

 be removed, the power of the other will occasion a continual automatic move- 

 ment, the removal of the Corpora Striata causing an irresistible tendency to 

 forward progression, whilst the division of the peduncles of the Cerebellum 

 (according to him) occasions the reverse movement. These assertions, however, 

 have not been confirmed by other experimenters. According to Longet (Op. cit.), 

 Schiff, 3 and Lafargue, 3 the results of removal of the Corpora Striata with the 

 anterior part of the Cerebral hemispheres are for the most part negative ; for 



1 Roser's und "VVunderlich's "Archiv. fur Physiol., Heilkunde," 1846, 667. 



2 "De vi motoria baseos encephali," Bockenhemii, 1845. 



3 "Essai sur la valeur des localisations encephaliques," &c., These inaug., Paris, 1838. 



