704 THE CEREBRAL CORTEX. 



in the higher animals, an important part, so that in them the cutting of it 

 off from the lower centre cells removes a great part of the impulses by which 

 they are normally stimulated. 1 



EFFECTS OF EEMOVAL OF ONE HEMISPHERE. 



G-oltz has published 2 several accounts of dogs with very extensive 

 lesions of the hemispheres, or from which one cerebral hemisphere has 

 been wholly removed. 3 Such animals, if kept a sufficient time after the 

 removal, show in their ordinary movements an extraordinarily slight 

 amount of motor paralysis, 4 although apparently rendered incapable of 

 performing such a purely volitional acquired action as the giving of the 

 paw. Some of the differences of movement which are observable can 

 be explained by the blindness which is produced on the homony- 

 mous half of the retina ; but the contractions of muscles of the opposite 

 side are rather less powerful than those of the same side. 6 Sensation 

 on the opposite side of the body is not lost, although somewhat blunted, 

 and even the muscular sense of the paralysed side appears to be 

 still present. Whether the recovery of movement and of sensation 

 which occurs in such an animal after a certain period, is due to a 

 representation of both sides of the body in each cortex (as is unquestion- 

 ably the case with the movements of some parts), and a vicarious taking 

 up of the functions of the lost side by the other hemisphere, or whether 

 the movements are merely association movements, which are called into 

 play through commissural fibres in the lower centres, is still uncertain. 

 It has, however, been ascertained in the dog and cat as well as in the 

 monkey, that what is believed to be the volitional tract in the cord 

 (crossed pyramidal tract), although mainly formed of fibres from the 

 opposite hemisphere, also contains fibres which come from the homony- 

 mous hemisphere, 6 and it may be through these fibres that such 

 volitional movements as are preserved are carried on. Unilateral 

 removal of the cerebral cortex, including the corpus striatum, is followed 

 by degeneration and atrophy in specific parts of the lower portions of 

 the central nervous system, which are either primary, resulting directly 

 from removal of the nerve cells from which descending fibres originate, 

 or from section of nerve fibres causing degeneration in their cells of 



1 Cf. Sherrington ("Proc. of Physiol. Congress," 1892, Centralbl. f. PhysioL, Leipzig u. 

 "Wien, Bd. vi. S. 399), who found in the monkey that the reflex flexion of the hallux, which 

 is caused by stimulation of the posterior roots of the sacral nerves, is abolished on cutting 

 through the cervical cord. 



2 In the Arch. f. d. ges. PhysioL, Bonn, Bde. xiii., xiv., xx., xxvi., xxviii., and 

 various other volumes up to the present time. An account of such an animal by Goltx, and 

 a report on the condition of the brain by J. N. Langley and A. S. Griinbaum, will be found 

 in the Journ. PhysioL, Cambridge and London, 1890, vol. xi. p. 606. Cf. also Vitxou, 

 Arch, de physiol. norm, etpath., Paris, 1892, tome v. 



3 For observations upon the frog with one hemisphere and the corresponding thalanms 

 removed, see Kato, "Thesis," Berlin, 1886 ; upon the pigeon see Lussana and Lemoigne, 

 " Fisiologia d. centri nervosi encefalici," Padova, 1871, and M'Kendrick, loc. ciL; on the 

 cat, R. Boyce, Phil. Trans., London, 1895, B, p. 321; and upon the rabbit (anatomical), 

 Miinzer and Wiener, Pray. med. Wchnsclir., 1895 ; Monatschr. f. Psychiat. u. NeiiroL, 

 Berlin, Bd. iii. S. 379. Frogs and pigeons show scarcely any noticeable defects, after 

 recovery from the immediate effects of the operation, and rabbits relatively little. There is 

 normally a tendency in moving to pass towards the side opposite to the lesion. 



4 Immediately after the removal there is hemiplegia and hemianaesthesia, but this is 

 gradually recovered from. 



5 Boyce, Phil. Trans., London, 1895, B. This result was obtained with the contrac- 

 tions produced by absinthe, which stimulates the cortical centres. 



6 See article "Spinal Cord," by Sherrington, in this volume. 



