x THE FOKE-BKAIN 595 



and those of the posterior segment with the temporo- occipital 

 region. 



Besides these fibres which unite the cerebral cortex with 

 subcortical centres the internal capsule contains many other 

 bundles : as those which unite the corpus striatum with the 

 thalamus arid those which connect the cortex with the thalamus. 

 Eeference should be made to the most recent text-books of the 

 anatomy of the nerve-centres for the origin, arrangement, and 

 course of this very complex system of projection and association 

 fibres. 



The nuclei of the corpus striatum, unlike those of the optic 

 thalamus, are not in close connection with the cerebral cortex. 

 This was clearly brought out by Gudden (1872), who found that 

 after extirpation of the sigmoid gyrus in the dog there is marked 

 atrophy of the thalamus, while the caudate nucleus and putamen 

 undergo only a slight diminution in size (Bianchi and d'Abundo). 

 Many of the projection fibres that run from the corona radiata to 

 the internal capsule also run through the corpus striatum, but are 

 connected with it only by slender collaterals, the principal branches 

 running to the grey matter of the thalamus, pons, bulb, and cord. 

 This different relation in which the cortex stands to the corpora 

 striata which form part of the prosencephalon, and to the optic 

 thalami which belong to the diencephalon. or 'tween brain, 

 harmonises with the theory which holds the basal nuclei to be an 

 integral and complementary part of the cortical system in general, 

 and particularly of the sensory-motor sphere. 



The physiological significance of the basal nuclei was the 

 subject in the past of very discordant hypotheses, iwhich were 

 either pure speculation or were based on inadequate anatomical, 

 clinical, and experimental observations, which need not now 

 concern us. Disease confined to the grey matter of the caudate 

 and lenticular nuclei, without lesions of the fibres of the internal 

 capsule, are rare, and not always properly observed and described 

 in the patient's lifetime. Experimental lesions of these nuclei, 

 owing to their position and connections, inevitably involve damage 

 to 'surrounding parts. This explains why the physiology of the 

 corpora striata is still rudimentary. 



It is possible indirectly to form an approximately correct 

 conception of the functions of the corpora striata, by comparing 

 the defect phenomena which ensue on extensive extirpation of the 

 cerebral cortex of the dog, including the whole sensory -motor 

 area, with those seen after complete destruction of the cortex and 

 also of the corpora striata. In our 1878 memoir (with Tamburini) 

 on the sensory -motor area of the dog, we put forward the 

 hypothesis in order to account for the partial and fairly rapid 

 compensation of the paralytic symptoms that the basal ganglia 

 were capable of vicariously assuming the functions of the excised 



2 Q 1 



