9 i8 THALAMUS OPTICUS. 



any rate, more than a hemianopia, 1 i.e. a hemianopia plus amblyopia of 

 the whole field. The hemianopia does not involve the central region of 

 the visual field of either eye. Severance of corpus callosum leads to no 

 permanent objective impairment ; 2 Ferrier and Turner and Lo Monaco, 

 making use of this fact, have proceeded to open the lateral ventricle sub- 

 sequent to partial section of corpus callosum, and with the thalamus well 

 exposed have destroyed the posterior part of it. There resulted total 

 blindness of the contralateral eye, impairment of tactual and dolorous 

 sensitivity in the crossed half of the body, and slight defect of force in 

 movements executed by the contralateral limbs. In Hughlings Jackson's 

 case, muscular weakness on the crossed side was noted. Symptoms both 

 in the dog 3 and monkey 4 abate in the course of some weeks ; the total 

 crossed blindness becoming amblyopia. The hemianopia and defect of 

 power of skin localisation appears permanent. The older observers 5 

 on experimental thalamic lesion obtained very regularly great disturb- 

 ance of motility, such as forced movements of various kind and degree. 

 It was in experimenting on the thalamus that Magendie discovered the 

 forced movement which he styled mouvement de manSge (circus move- 

 ment). Eecent 6 observers have not confirmed " forced movement " as 

 a necessary part of the symptomatology of thalamic lesion. Neither is 

 paralysis ; the utmost impairment of the motor power amounting only 

 to a slight hemiparesis. Many observers 7 have noted signs of disturb- 

 ance of the muscular sense. 



The effects of removing the cerebral hemispheres, either along with 

 or without simultaneous removal of the diencephalon, have already been 

 described (see article, " Cerebral Cortex "). In both cases there is loss of 

 intelligence, in higher mammals imbecility. There is a great difference 

 between the animal without telencephalon but with diencephalon, and the 

 animal deprived of both telencephalon and diencephalon, especially in 

 regard to the facility and completeness of performing complex muscular 

 movements. The most plausible explanation seems that which supposes, 

 that with diencephalon remaining there is still possible a conjoint 

 influence of visual impressions with impressions derived from other senses 

 (tactual, muscular, and labyrinthine), which makes itself felt upon the 

 machinery of the skeletal musculature : when the diencephalon is lost, 

 the contribution from the retina largely disappears. 



Experimental lesions of the thalamus cause distinct rise of body tempera- 

 ture, apparently without vasomotor disturbance. 8 



One territory of the thalamus (corp. genie, lat.) functions as a station 

 between relay cells from the nerve cells (retinal) of vision and nerve 

 cells conducting through the " optic radiations " to the visual field of the 



1 Ferrier and Turner, Lo Monaco. 



2 Koranyi, Arch. f. d. gr.s. Physiol., Bonn, 1890, Bd. xlvii. S. 35 ; Muratoff, Neurol. 

 Centralbl., Leipzig, 1893, Bd. xii. S. 714 ; Lo Monaco (Luciani's Laborat.), Riv. di 2>atol. 

 nerv., Firenze, April 1897. 



3 Lo Monaco, Arch. ital. de biol., Turin, 1898, tomo xxx. p. 198. 



4 Ferrier and Turner, Phil. Trans., London, 1897, vol. clxxxix. 



5 Magendie, Longet, Schiff, Renzi, Lussana and Lemoigne. 



6 Nothnagel, Virchows Archiv, Bd. Ixii. S. 201 ; Ferrier, "Functions of the Brain," 

 lot. cit.; Ferrier and W. A. Turner, Phil. Trans., London, loc. tit.; Lo Monaco, loc. cit.; 

 Sellier and Verger, loc. cit. 



7 Meynert especially insisted on this. See also Ferrier, " Functions of the Brain," 1876, 

 p. 248. 



8 Hale White, Lancet, London, 1891, vol. ii. ; Tangl, Arch. f. d. gcs. Physiol., Bonn, 

 1895, Bd. lxi. S. 559. 



