134 



ANATOMY OF THE CENTRAL NEETOUS STSTEM. 



In the geniculatum a part of the optic nerve ends in striking ramifica- 

 tions in whose midst are the dendrites of elongated fusiform cells whose 

 median end ramifies within a bundle which probably^ also, belongs to the 

 optic system. These structures are well represented in Fig. 81. 



In the midst of all these ganglia end the Tr. thalamo-hulbares et spinales. 

 It is, however, still impossible to designate just what nucleus is the terminal 

 one (see Fig. 64, Bad. Thai). 



With the mention of the Nuc. entopeduncularis, a group of large gan- 

 glion-cells median to the Tr. strio-thalamici, I have enumerated the most 

 important ganglia characteristic of the thalamencephalon of lower verte- 

 brates. 



Fig. 83 shows a schematic representation of the nuclei of the thalamus 



Fig. 83. — Schema of the principal nuclei and tracts of the interbrain of the pigeon. 



in the pigeon. It gives a good general idea of the structural relations 

 already quite complicated in birds and as yet not well known. 



What is recognized as common to the nuclei of the thalamus in all 

 lower vertebrates may be thus summarized: The nuclei of the interbrain 

 receive fibers from the basal ganglia of the forebrain, and give off posteriorly 

 new tracts to centers ivhich lie at a lower level. Furthermore they are joined 

 to the ganglia of the hypothalamus in manifold combinations. The fibers 

 which pass to the roof of the midbrain and to the medulla and spinal cord 

 have already been mentioned. We will soon find that also from the nuclei 

 of the hypothalamus tracts lead to the cerebellum and to other regions of 

 the midbrain than to the roof. So we see in the thalamencephalon a great 



