

Functions of the Basal Ganglia. 629 



designated is not related to the optic sense exclusively, and is not an 

 optic organ in any such sense as are the corpora quadrigemina. The 

 optic thalami of birds or mammals may be destroyed without; destroying 

 sight or the activity of the pupil, neither does irritation of either of 

 them produce contraction of the pupil. The optic thalamus is more or 



FIG. 348. Horizontal section of the Op- 

 tic Thalami of the Rabbit Just above the 

 level of the internal capsule. 



1. Median nucleus. 



2a. Anterior cell group of Tuberculum 

 Anterius. 



2b. Posterior cell group of Tuberculum 

 Anterius. 



3. External nucleus. 



4. Cancellated layer. 



5. Corpus geniculatum externum. 



6. internum. 



7. Posterior nucleus of the Optic Thal- 

 amus. 



From Ferrier, after Monakow. 



less directly continuous with the 

 tegmentum or the posterior one- 

 third, the sensory division of the 

 crura cerebri ; and the cutaneous 



sensory tracts of the internal cap- FlG 348 



sule are in connection with the optic thalami. The optic tracts, or con- 

 tinuations of the optic nerves, are connected with the pulvino-geniculate 

 portion of the thalamus. The thalamus is also connected, by way of 

 the pillars of the fornix, with the centers of smell, tactile sensibility, 

 and probably taste, in the cortex of the cerebrum. It also connects, by 

 means of the corona radiata, with the sensory occipito-temporal portion 

 of the cortex. (Fig. 366, T4> ) It also connects with the corpora stri- 

 ata, and is supposed to communicate through the frontal part of the 

 cortex by fibres ending in the gyrus fornicatus (fig. 366, /.), and is 

 connected with the region of the insula, and with the hippocampal re- 

 gion directly by way of the pillars of the fornix, or indirectly via the 

 corpora mammillaria. 



The optic thalamus is exclusively sensory, and is believed to have no 

 motor functions at all. The stimuli that are condensed in it are for- 

 warded to other centers, the corpus striatum, the cerebrum, and prob- 

 ably the cerebellum, and are, in these organs, transformed into motor 

 currents. It is especially related to the visual tracts, but also receives 

 and forwards sense impressions from all the sensory organs. This is 

 proved by the fact that it is connected with all the sense centers of the 

 cortex of the hemispheres, to which there can be no doubt it forwards 

 its condensed and made up sense stimulations. Of the several roots of 

 the optic nerve in each optic thalamus, the ones originating with the 

 corpus geniculatum internum are not concerned in the sense of vision, 

 since they do not undergo atroph}^ as the other roots do when the eyes 

 are destroyed. They are supposed to answer as a commissure. The 



