ix MID- AND INTER-BRAIN 521 



to the operative methods employed and the greater or less lesions 

 of the adjacent parts. 



The anatomical connections of the thalami with the other 

 portions of the brain (pp. 489 et seq.) throw sufficient light on 

 this difficult subject. Anatomical research, particularly the most 

 recent work of Dejerine and of Roussy, has proved that every part 

 of the cerebral cortex receives nerve-fibres from the optic thalamus. 

 On the other hand, the thalamus sends no fibres to the cerebral 

 peduncle or to the bulb and spinal cord ; after destruction of the 

 thalamus no degeneration is seen either in the motor (pyramidal 

 tracts) or the sensory (lemniscus) paths. 



The atrophy of the thalamus that follows excision of the 

 opposite eyeball (Panizza, J. Svan) shows the extreme importance 

 of the thalamus in vision. In the lower vertebrates the corpora 

 bigemina represent the principal station reached by the fibres of 

 the optic nerve ; but in the higher vertebrates the thalamic visual 

 centres are always larger in proportion to those of the mid-brain 

 (Gudden, v. Monakow, Edinger, and others). Of the four masses 

 of grey matter into which the mammalian thalamus is divided, it 

 is the hindmost, the pulvinar, which directly receives the optic 

 fibres ; and the pulvinar and the external corpus geniculatum give 

 origin to the paths to the occipital region of the cortex and the 

 angular gyri (v. Monakow, Vialet, Ferrier, and Turner), which as 

 we shall see in the next chapter represent the cortical centres 

 of vision. 



Many fibres of the mesial fillet (lemniscus) terminate in the 

 lateral nucleus of the thalamus, and penetrate especially into its 

 ventral and posterior parts round the centre median of Luys. As 

 we know, this represents the continuation of the dorsal columns of 

 the spinal cord, and perhaps also Gowers' tract ; in a word, the long 

 spino-cerebral sensory paths. 



From the lateral grey matter of the thalamus, fibres run to the 

 parietal and mesial regions of the cortex ; those to the Rolandic 

 area receive their medullary sheath very early, towards the ninth 

 month of foetal life. The fibres that run from the anterior part of 

 the thalamus to the frontal region of the cortex are late in acquir- 

 ing their sheath (fourth month after birth). A large system of 

 fibres that develops early unites the thalamus to the nuclei of 

 the corpus striatum, that is, the caudate nucleus and lenticular 

 nucleus. Lastly, the thalamus receives fibres from the superior 

 cerebellar peduncle, either directly or through the red nuclei. 



These anatomical considerations as a whole naturally lead to 

 the conclusion that the thalamus is a great sensory centre, to 

 which a number of centripetal paths from different sensory organs 

 converge, and from which they spread out to the different regions 

 of the cerebral cortex. Broadly speaking, apart from exaggeration 

 and fancies, this was the theory sustained by Luys (1865-76) 



