THE CEHEBRUM OH PEOSENOEPHALON. 



157 



The higher Tertebrates — ^the birds and the mammals— manifest in the 

 structure of the corpus striatum an especial construction. In mammals it 

 is divided into a lateral and a median portion by fibers from the cerebral 

 cortex which bisect it. The lateral portion is designated as the Putamen 

 and the median portion as the Nucleus caudatus. Several ganglia — Globus 

 pallidus — lie on the median side of the Putamen, whose nature is not yet 

 understood, and which are so closely associated with the Putamen that they 

 are grouped with the latter and the whole ganglion-complex called the 

 Nuc. lentiformis. This will be more fully discussed subsequently. In birds 

 the Putamen and both portions of the Globus pallidus are demonstrable, but 

 the divisions of this portion of the striatum from the Nuc. caiidatus is not so 

 sharp as in mammals, because the fibers from the cortex which, as Gapsula 

 interna in mammals, separates the two portions are in birds only slightly 

 developed. Notwithstanding that, one can with certainty recognize in birds 



Fig. 105. — Schematic frontal sections of the forebrain, to show the position 

 of the striatum and its fiber-system in relation to the whole. A, Brain of a 

 Teleost; B, of a Bird; C, of a Mammal. 



that from the Putamen, located extremely laterally, a thick bundle passes 

 inward, where it meets those fibers which arise in other parts of the striatum. 

 The two bundles together pass to the nuclei of the thalamus (see Pigs. 83, 

 84, and 104). 



Thus the Tr. strio-thalamici are composed in the bird, as in the mam- 

 mal, of a median bundle and of one which joins it from the outer side. 

 The lateral bundle includes in mammals the greater part of the fibers of the 

 cerebral base which pass down from the cortex. It is there called the 

 "loop" of the Nucleus lentiformis. The median portion corresponds in birds 

 and mammals according to its position exactly the same as is shown in Fig. 

 103 for the fish-brain. Thus it belongs to that collection of fibers which 

 is designated as the Capsula interna. 



