io8 BRAINS OF RATS AND MEN 



similarly is differentiated in situ and not infolded from the ventral 

 margin of the pyriform cortex. The end result, however, in the 

 adult brain of Sphenodon is substantially the same as in the 

 turtle. 



Quite apart from questions of embryological development of 

 these parts, it seems clear that in adult reptilian brains the hypo- 

 pallium is transitional tissue between the older part of the corpus 

 striatum and the neopallium and that the amygdaloid ridge is 

 transitional betwen the primitive amygdala and the differentiated 

 pyriform cortex. With further development of these cortical 

 sheets in mammals, the dorsal ventricular ridge loses its anatomi- 

 cal separateness. In embryonic mammals (Hines, 1922) the 

 reptilian form of corpus striatum complex is repeated almost 

 exactly, but in the adult the anterior end of the dorsal ventricular 

 ridge (hypopallium) is joined to the olfacto-striatum to form the 

 caudate nucleus and its posterior end (amygdaloid ridge) is joined 

 to the amygdala. The lentiform nucleus (putamen and globus 

 pallidus) is separated from the caudate nucleus by internal cap- 

 sule fibers. 



In birds the hypopallium is probably represented in the 

 hyperstriatum (Fig. 19, p. 96) which Kappers (1923) has shown 

 is derived embryologically from pallial territory and which per- 

 forms functions closely related with those of the cerebral cortex. 



From the preceding account it follows that the human cau- 

 date nucleus is a mixture of elements of two very diverse sorts: 

 (i) a very ancient olfacto-striatum, primitively developed within 

 the lateral olfactory nucleus; and (2) beginning with reptiles 

 the addition of other elements from a non-olfactory field more 

 intimately related with the neopallium. The amygdala has a 

 somewhat similar history. Primitively developed within the 

 caudal end of the lateral olfactory nucleus, there are added to it 

 in reptiles other elements from a field intimately related with the 

 pyriform cortex which is now highly differentiated. In the human 

 caudate and amygdala the non-olfactory functions clearly pre- 



