530 THE ORGANS 



ventrally, so that the libres from the ventral parts pass to the 

 ventral part of the central region of the pallium, dorsal to dorsal, 

 etc. (E. Sachs.) 



The nuclei of the internal segment of the thalamus do not appear, 

 according to some recent researches, to have direct connections with 

 the cortex palHi. The anterior nucleus receives the bundle of Vicq d' 

 Azyr (mamillo-thalamic tract) and probably sends libres to the 

 nucleus caudatus (see p. 539). It thus belongs to the olfactory 

 apparatus. The median nucleus is also probably connected with 

 the nucleus caudatus. The median center of Luys and the nucleus 

 arcuatus send fibres to adjoining thalamic nuclei, especially the lateral 

 nuclei, and appear to be thus association nuclei. Other authorities 

 afhrm that ascending tracts are received by some of these internal 

 nuclei and that they have direct cortical connections. Descending 

 tracts coming directly from the thalamus have not been definitely 

 demonstrated. 



PRACTICAL STUDY 



II. Transverse Section through the Junction of Midbrain and Thalamus. 



(Figs. 332 and 356.) 



The most conspicuous change from the last section is the appearance, or 

 increase, of the geniculate bodies and pulvinar, and the thalamic radiations. 



Efferent Peripheral Neurones. — The nuclei and root fibres of the III nerve 

 are still present. 



Afferent Roots, their Terminal Nuclei, Secondary Tracts, and Tertiary 

 Neurones. — The fibres of the optic tract (optic "nerve") are seen entering the 

 ventral surface of one of their terminal nuclei, the lateral or external geniculate 

 body. Other optic fibres (not entirely traceable) enter the pulvinar thalami and 

 the superior colliculus {Stro) (see also preceding section). On the dorso-lateral 

 surface of the lateral geniculate body, a bundle of fibres accumulates which 

 represents the beginning of the geniculo-calcarine tract to the occipital cortex, 

 thereby completing the visual path. 



Internal to the lateral geniculate body is the medial (internal) geniculate body 

 which now contains the terminals of the brachium of the inferior colliculus. 

 Fibres from its cells gather on its lateral surface. These represent the beginning 

 of the geniculo-temporal tract to the temporal cortex, thereby completing the 

 auditory path. 



Internal and ventral to the medial geniculate body are the medial lemniscus 

 (bulbo-thalamic) and spino-thalamic tracts about to terminate in the ventro- 

 lateral thalamic nuclei whose axones complete the general sensory path by passing 

 to the central cortex. 



The central tegmental tract can hardly be distinguished. 



Intersegmental Neurones. — The nucleus ruber is still large, but the remainder 





I 



