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HANDBOOK OF PHVSIOLOGV 



NEUROPHYSIOLOGY II 



white = agranular cortex 



granular cortex poor in 



granule cells 



wranulor cortex increas- 

 [ I ' 1 s ingly ricti in granule 



granulous cortex (konio- 

 cortex) 



FIG. I. Distribution of agranular (while) and different 

 types of granular and granulous cortex in man, according to 

 von Economo. [From von Economo (-261).] 



arcuate convolutions, taken together, were earlier 

 designated the cingulate (261) or fornicate gyrus 

 (205, 206), the limbic lobe (249) or the grand lohe 

 limbique (34, 35). The latter term also includes other 

 structures (cf. below). 



Posteriorly the two gyri are continuous in the retro- 

 splenial region. Anteriorly the cortex of the posterior 

 orbital surface of the frontal lobe, the anterior insula 

 and adjacent temporal pole is interposed between the 

 anteroventral ends of the two convolutions, thus 

 completing a cortical ring around the rostral brain 

 stem and interhemispheric commissures. Closely asso- 

 ciated with these convolutions is the hippocampus 

 proper. Based on phylogenetic studies Herrick (100) 

 made a distinction between 'archipallium' (hippo- 

 campus, fascia dentata and subiculum), 'paleopal- 



lium' (pyriform cortex cosering the anterior portion 

 of the hippocampal gyrus) and 'neopallium.' The 

 archi- and paleopallium are covered by an ancient 

 type of cortex termed allocortex (259). The grey 

 matter of the rest of the ring-like formation forms a 

 'transitional' cortex, also termed 'juxtallocortex,' 

 which separates the typical alio- and isocortex. Part of 

 this juxtallocortex has also been designated 'meso- 

 cortex' (for references cf. 126, pp. 72-86; 202). 



The general concept of most morphologists has 

 been that all these alio- and juxtallocortical structures 

 are concerned with important olfactory functions and 

 they formed the basis for Broca's (34) delimitation of 

 his grand lobe limbique. The anterior part of the cingu- 

 late gyrus was specially designated as le centre olfaclif 

 superieur. All these structures have also been variously 

 included in the ill-defined terms 'rhinencephalon' or 

 'olfactory brain.' Subsequent anatomical and physio- 

 logical research has not given any support to the pre- 

 sumed olfactory function of the cingulate region, the 

 hippocampus and some other parts of the 'limbic 

 lobe' (see 36, 126, 162, 184, for review and references). 



More recently Broca's term "limbic lobe' has been 

 adopted by MacLean and others (162, 163, 166). 

 The cortex of the posterior orbital surface of the 

 frontal lobe, the anterior insula and the temporal 

 polar region which, by Broca's definition, would be 

 outside the 'limbic lobe" (because it is peripheral to 

 the rhinal fissure) has, on accovmt of its close cyto- 

 architectural (260, 261) and functional (126, 133) 

 similarities to the adjacent alio- and juxtallocortex, 

 also been included. At our present state of knowledge 

 the term 'limbic lobe' is, in the reviewers opinion, 

 of doubtful value, even though it is convenient. The 

 same applies to the still broader term 'liinbic system' 

 (10, 76, 164, 166) which, in addition to the cingulate 

 and hippocampal gyri, the hippocampus, and the 

 orbitoinsulotemporal polar region, includes all the 

 subcortical cell stations presumai^ly associated with 

 the 'limbic lobe' (amygdala, septal nuclei, hypo- 

 thalamus, epithalamus, anterior thalamic nuclei, and 

 parts of the basal ganglia) (163, 166). Although the 

 cortical areas contained in the 'limbic lobe" may share 

 some structural characteristics, it is not known 

 whether they form a functional unit. Recent anatomi- 

 cal and physiological research rather tends to fraction- 

 ate the "limbic system' into .several units with quite 

 different projections and functional significance. We 

 shall return to this important question at the end of 

 this chapter. 



The areas to be dealt with in this .section, viz the 

 anterior cingulate, posterior orbital, anterior insular 



