1^6 JouRXAi. OF Co:mparative Neurology. 



mals which is called trigonum habenuhe is found in the 

 fishes. The thalamencephalon in the fishes seems indeed to 

 be of small importance; it appears in many of the species 

 as if it were a mere band of nerve-tissue, connecting the 

 prosencephalon with the mesencephalon. In the amphibians 

 and also in the reptiles the development of this part of 

 the brain is carried further; not that the relative size is 

 so much greater, but that the fibre connections are more 

 complex. The general arrangement of the parts is more sug- 

 gestive of that of the lower mammals. In the birds the 

 thalamencephalon is perhaps as well developed as in the rep- 

 tiles, but relatively to the other structures is not deemed of 

 such importance, partly because the corpora striata are 

 so much larger than in the preceding type, and also because 

 of the enormous size of the optic lobes. 



Relations to Cerebral Tracts. — We shall now consider the 

 relation of the thalami to the basal prosencephalic tract, and 

 at the same time, their relations to the bundles of fibres con- 

 necting them with the cerebellum, the medulla oblongata, 

 and the optic lobes. 



With regard to the teleosts, Mayser [' p. 322, et seq.J says 

 that the connection of the valvula cerebelli with the inferior 

 lobes is very distinct. After the tract reaches the inferior 

 lobes, it becomes dorsal to, and spreads over the part con- 

 necting the inferior lobe and the pars peduncularis. Some 

 of the fibres divide oft', and go to the cerebellar tract. This 

 is somewhat the same view as that of Bellonci, for he con- 

 siders [^ p. 24] that the inferior lobes are really parts of what 

 he, in his researches, calls the inner and the outer commis- 

 sures. Goronowitsch also states [''' p. 545, et seq.] with 

 regai-d to the teleosts, that the tract running through the 

 base of the mesencephalon and ending in the region of 

 the thalamencephalon is perhaps homologous to the tract in 

 the subthalamic region of the higher vertebrates. 



In the amphibian brain [Osborn,'" p. 78] the bundle 

 of fibres composing the dorsal portion of the cerebral 



