MOVEMENTS OF THE TRUNK AND TAIL. 745 



improvement, and movements return, so that after a few weeks the 

 animal climbs and runs about apparently as usual. Probably, however, 

 the movements are now " associated " with those of the opposite side, 

 and not truly voluntary ; for if such an animal, apparently completely 

 recovered, be held by the upper part of the body and lowered suddenly 

 to the ground, or swung towards a cage, the leg which was paralysed is 

 never put down to meet the ground or forwards to catch hold of the 

 cage, a movement which is always made by an unparalysed leg. 

 Sherrington x has shown that in the monkey stimulation of a point 

 in the posterior part of the lobus paracentralis, on the mesial surface, 

 causes contraction of the sphincter ani. 



5. The area for movements of the trunk and tail. — This is a 

 comparatively small area, lying chiefly on the marginal convolution (Fig. 

 338) 2 in front of the leg area, but coming to the external surface (Fig. 

 336) and extending over a small portion of the superior frontal gyrus 3 

 as far as the limit of the arm area, which here bounds it laterally and 

 anteriorly. 4 



Its excitation is followed by a bending of the tail to the opposite 

 side, combined with a bending of the trunk or a rotation of the pelvis. 

 The area is too small to give any well-marked differentiation on analysis 

 by stimulation, but, on the whole, it is noticeable that the posterior 

 part is especially connected with the movements of the lower part 

 of the trunk and pelvis, associated with hip and leg movements ; 

 the anterior part with movements of the upper part of the vertebral 

 column, associated with shoulder and arm movements. The trunk 

 movements are occasionally bilateral, the tail or vertebral column being 

 extended. Extirpation of the trunk area on one side produces, unless 

 the lesion involve the adjacent areas (which it is somewhat difficult to 

 avoid), very little obvious effect. If, however, it be removed on both 

 sides simultaneously, there is for a time complete inability to sit erect, 

 power over the trunk muscles being entirely lost. 5 



The motor centres in the anthropoid apes.— These have only been 

 determined in a single case (orang-utan), 6 and by the method of 

 faradic excitation, but since the configuration of the brain in the 

 anthropoids approaches still more closely to that of man than does that 

 of the monkey, the evidence afforded is of great value and interest. It 



1 "Proc. Physiol. Cong.," Gcntralbl. f. Physiol., Leipzig u. Wien, 1892, Bd. vi. 

 S. 399. 



2 Horsley and Schafer, Proc. Roy. Soc. London, 1884, vol. xxxvi. 



3 Ferrier, ibid., 1875 ; Horsley and Schafer, Phil. Trans., London, 1888, B, p. 9. 



4 On the centres for the trunk muscles in dogs, see Unverricht and Kusick, Ges. 

 Abhandl. d. Tried. Klin, zu Dot-pat, Wiesbaden, 1893 ; and H. Werner, Allg. Ztschr. f. 

 Psychiat., etc., Berlin, 1895, Bd. lii. S. 134. These authors failed to confirm Munk's 

 statement, that the centre for the trunk muscles is in the frontal lobes. They find that 

 it lies between the centres for the muscles of the fore- and hind-limbs, and that its ex- 

 citation provokes movements of the trunk muscles of the same side. Rothmann (Neurol. 

 Centralbl., Leipzig, 1896, S. 1105) states, however, that the trunk movements described by 

 those authors are really passive, and are due to contractions of hip and shoulder muscles of 

 the opposite side. Rothmann, who examined the brains of four dogs from which Munk 

 had removed the prefrontal lobe of one side, was unable to find any descending degenera- 

 tion in the pyramidal tract either at or below the medulla oblongata. It is therefore 

 highly improbable that the centre for the trunk muscles is in this part of the dog's 

 brain, as taught by Munk. 



5 Horsley and Schafer, Phil. Trans., London, 1888, B, p. 13. This condition was 

 not recovered from in the animals we operated on, but they were not kept under observation 

 for more than three or four weeks. 



6 Beevor and Horsley, Phil. Trans., London, 1890, B, p. 129. 



