THE CBEEBEUM OR PEOSENCEPHALON. 



155 



This tract has already been encountered in the description of the interbrain. 

 A careful review of Figs. 72 and 80 will be profitable in this connection. 

 Through the Tr. strio-thalamici the basal ganglia of the forebrain are 

 most intimately connected with the ganglia of the interbrain. These tracts 

 are exceedingly constant, and, though they are recognized with especial ease 

 in teleosts because of the lack of other fiber-systems from the forebrain, 

 yet it is possible to demonstrate them in amphibians (Figs. 75 and 80), in 

 reptiles (Figs. 72, 81, and 82), in birds (Figs. 83 and 84), and in mammals. 

 They are naturally less prominent in the last, where the fiber-s.ystem from 

 the cortex to the interbrain and to parts of the brain located still farther 

 posterior is especially highly developed. Their discovery was first made 



Fig. 103.- — Diagrammatic frontal section through tlie brain of a turtle 

 (left) and of a lizard (right). 



possible through embryological methods; later, also, through the study 

 of degenerations. If one remove the whole mantle from a dog's brain, — a 

 feat successfully accomplished by Monakow on the newborn animal and by 

 Goltz on the adult,- — all the bundles which arise from the mantle degenerate, 

 and those which arise from the striatum remain intact. In the stained 

 section these are brought out into prominence. In Fig. 102 it has been 

 attempted to make the mantle more clear by inscribing a section through 

 the corpus striatum of a teleost within the contour of a human brain. 

 One sees at once that the fiber-system of the striatum falls in the region 

 which in mammals is designated as the anterior limb of the Oapsula in- 

 terna. In the teleost the thin mantle is insignificant in comparison to the 

 striatum; in mammals the relation is nearly reversed; but in birds, where 



