I02 BRAINS OF RATS AND MEN 



The reptilian cerebral hemisphere includes in front the large 

 olfactory bulb, into which the olfactory nerve discharges directly 

 from the nasal epithelium. Immediately behind this is a field of 

 reflex correlation dominated by the fibers of the olfactory tracts 

 coming from the bulb, the olfactory nucleus. The ventromedial 

 wall is the septum, a center of olfactory, gustatory, and visceral 

 correlation. The massive ventrolateral wall contains the corpus 

 striatum and amygdala, both of which are very complex internal- 

 ly. The striatum complex includes a number of structures which 

 can be recognized as the precursors of the mammalian globus 

 pallidus, putamen and caudate nucleus, though these parts are 

 not assembled in the mammalian pattern. The amygdala lies 

 posteriorly of the striatum and is very large and complicated in 

 reptiles and lower mammals, though in man it is reduced to a 

 small gray nucleus under the temporal lobe of the hemisphere. 

 These are all subcortical structures. The dorsal convexity is 

 occupied by the three cortical sheets to which reference has 

 already been made. The relations of these parts in the brain of 

 the turtle will be described in some detail, following in the main 

 the studies of Johnston (191 5, 1923). 



Figures 20-24 are outlined from Johnston's figures, but the 

 names applied to the parts are in some cases changed in con- 

 formity with the present text. In reading the literature of fore- 

 brain structure of lower vertebrates it must be borne in mind that 

 the terms corpus striatum, epistriatum, paleostriatum, archi- 

 striatum, neostriatum, hypopallium, etc., are used in different 

 senses by various authors and that all of these usages are based on 

 inadequate knowledge of the actual functional connections of the 

 parts in question. Some parts of the forebrain can be recognized 

 from fishes to mammals without fundamental change; other 

 parts are profoundly modified, and the application of mammalian 

 names to these latter parts is apt to be confusing. 



For purposes of orientation we may first sketch in outline 

 the probable history of the evolution of the strio-amygdaloid 

 complex in vertebrates. 



