CORTEX AND CORPUS STRIATUM 103 



Primitively, as in cyclostome fishes, all of the endbrain 

 (telencephalon) probably received olfactory fibers, with the ex- 

 ception of a small field (the "somatic area" of Johnston or "stri- 

 atum" of current descriptions of cyclostomes) adjacent to the 

 thalamus. This so-called striatum also receives fibers from ol- 

 factory correlation centers, though not directly from the ol- 

 factory bulb, and throughout the fishes the corresponding field is 

 broadly connected by ascending and descending fibers with the 

 thalamus. This field may be called the "primordial striatum." 



In most fishes and in the lower Amphibia the primordial 

 striatum is very imperfectly separated from the adjacent second- 

 ary olfactory nuclei. It is included within the somatic and olfacto- 

 somatic areas of my analysis (1922^). In the dogfish and the 

 frog it is tolerably clearly subdivided into two parts: First, 

 there is the somatic striatum, whose dominant ascending and 

 descending connections (exteroceptive in function) are with the 

 thalamus, but which also receives correlation fibers from olfactory 

 centers of the hemisphere. This is the "somatic area" of Johns- 

 ton, the precursor of the lentiform nucleus. Second, there is a 

 complex which serves correlations of olfactory nervous impulses 

 with those of taste, general visceral sensibility and others, the 

 olfacto-striatum and primitive amygdala. This was originally 

 differentiated within the lateral olfactory nucleus under the in- 

 fluence of fibers ascending from the hypothalamus and thalamus. 

 This complex is under strong olfactory influence throughout the 

 vertebrate series; in mammals it becomes part of the caudate 

 nucleus and part also of the amygdala. 



In reptiles Johnston in 1923 called the olfacto-striatum the 

 "bed nucleus of the stria terminalis." Jt is the deepest part of 

 the striatum complex (Figs. 21, 22, 23), extending nearly the 

 whole length of the hemisphere close to the ventricle and ter- 

 minating behind in the highly diff"erentiated primitive amygdala 

 (Fig. 24). The somatic striatum, or lentiform nucleus, Hes more 

 laterally and is clearly separated into putamen (an aflferent cen- 

 ter, Figs. 20, 22, 23) and globus pallidus (an efl^erent center. Fig. 



