156 



ANATOMY OF THE CENTRAL NERVOUS SYSTEM. 



the corpus striatum reaches remarkable size, it makes the major part of the 

 forebrain, notwithstanding the presence of a fairly deTeloped mantle. 



In turtles the enormous development of the basal ganglia, especially 

 the development of a mesostriatum, and of the epistriatum and the disap- 

 pearance of the lateral horns of the ventricle makes a cross-section which is 

 completely different from the brain of other reptiles, and reminds one 

 strongly of the bird-brain (study Pig. 103). 



The chelonian brain, with its enormous basal ganglia and slight de- 

 velopment of the mantle, is more like the avian brain than is any other 

 reptilian brain. 



The Corpus striatum of birds and mammals is, up to the present, well 



Fig. 104. — Frontal section through the brain of a parrot. A somewhat schematic 

 composite of several serial sections into one figure. 



known only in its principal features; much yet is lacking to furnish a clear 

 understanding of it, especially in its subdivisions. The author's experiments 

 in degeneration show one thing, however: Xeither in reptiles, in birds, 

 nor in mammals can one through removal of the corpus striatum cause 

 degeneration of parts posterior to the midbrain. This indicates that thai 

 important and constant structure, the striatum, confines its efferent fiber- 

 system essentially to the thalamus and the hypothalamus. The individual 

 bundles of the strio-thalamici are developed to a varying degree, according to 

 the size of the thalamic ganglia to which they go. For example, the bundle 

 to the large hypothalamus in the teleost is enormous, — Tr. strio-hypothala- 

 mus, — while in other animals it is often difficult to find. 



