1396 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY' II 



FIG. I. Nuclear subdivisions of the amygdala 

 in different mammalian species (Nissl stain). 

 .1.- opposum; B: cat; C man. (.,4, B and C are 

 all frontal sections oriented in the same way 

 with medial to the right and lateral to the left. 

 V. in C indicates the tip of the temporal horn 

 of the lateral \'entricle.) A and B: L, lateral 

 nucleus; Bi, basal nucleus, lateral (large- 

 celled) portion; B,„, basal nucleus, medial 

 (small-celled I portion; C, central nucleus; M, 

 medial nucleus; and C«, cortical nucleus. C: 

 Apt with its subdivisions corresponds to the 

 lateral nucleus; Api„„f and Api„„ to the 

 lateral portion of the basal nucleus; Apv with 

 its subdi\isions and probably also Apip^ to the 

 medial portion of the basal nucleus; Apm with 

 its subdivisions to the accessory basal nucleus 

 which cannot be clearly identified in the opos- 

 sum and the cat; Asf and pA with their sub- 

 divisions to the cortical nucleus; prAirir to the 

 corticoamygdaloid transition area which can 

 be clearly identified only in primates; sApv and 

 perhaps sApd to the central nucleus. The medial 

 nucleus is represented by the area lateral to 

 psAi wedged in between sApd, Apm,„aci and 

 Asfid. \_A is a photograph of an original slide 

 in Dr. E. C. Crosby's collection. C is taken 

 from Brockhaus (31).] 



the nuclei as 'lateral,' 'medial,' etc., indicates their 

 position in low mammalian forms only (fi,?. i^). Due 

 to the expansion of the neopallium, the amygdala is 

 rotated in higher forms until finally in man the lat- 

 eral nucleus occupies a ventral and the medial nucleus 

 a dorsal position (fig. iA,B,C) (46, 132, 137). Parallel 

 to this there is a gradual reduction of the cortico- 

 medial complex and a continuing development and 

 differentiation of the basolateral complex which at- 

 tains its highest complexity in man (31, 46, 1 18). 



Ontogenetic and phylogenetic studies show that 

 the corticomedial and basolateral complexes have a 

 pallial matrix, whereas the corticomedial complex is 

 subpallial in origin (119, 132, 164). The corticomedial 

 complex is phylogenetically older and its primordium 

 can be traced back to the cyclostomes (48). A well- 

 circumscribed amygdaloid 'nucleus' appears first in 

 tailless amphibians, at which stage it originates in 

 parallel to the emergence of the vomeronasal organ of 

 Jacobson, from which, in these forms, it receives its 

 main afferent inflow {113). At this low evolutionary 

 level the general plan of efferent amygdaloid connec- 

 tions of higher forms is already laid down. One 

 system of fibers, including the dorsal olfactory pro- 



jection tract of Ramon y Cajal (208), crosses the lat- 

 eral forebrain bundle dorsally and reaches the septum, 

 the preoptic region and the hypothalamus; it corre- 

 sponds to the stria terminalis of higher forms which 

 swings dorsally around the enormously enlarged 

 lateral forebrain bundle, now called the internal 

 capsule. Another system of fibers runs from the 

 amygdala to septal and preoptic regions crossing the 

 lateral forebrain bundle ventrally. It corresponds to 

 the diagonal band of Broca and other less well- 

 defined ventral amygdalohypothalamic tracts of 

 higher forms running below the internal capsule. To 

 this primitive amygdala, which they inherited from 

 their ampliibian ancestors, the reptilians add a new 

 element of hypopallial origin. It forms the posterior 

 part of the dorsal ventricular ridge and probably 

 corresponds to the basolateral complex of mammals 

 (37- 45. 48, ii9> 132, 137)- 



.AN.^TOMIC.'kL .AND PHYSIOLOGICAL STUDIES 

 OF .AMYGD.ALOID CONNECTIONS 



Afferent Connections 



OLF.ACTORY CONNECTIONS .AND OLF.ACTORY FUNCTIONS 



OF .AMYGD.AL.A. Among the afferent connections of the 



