132 BRAINS OF RATS AND MEN 



the olfactory bulb (directly or indirectly) pervade the 

 medial walls of the cerebral hemispheres and most of 

 the lateral walls except for an area of variable size, 

 the somatic striatum, which seems to receive somatic 

 fibers exclusively. In higher forms the margins of the 

 cerebral cortex (archipallium) have strong olfactory 

 connections. The dorsal cortex (neopallium), on the 

 other hand, is dominated by its thalamic connections. 

 The olfactory field (both cortical and subcortical) also 

 receives numerous ascending fibers of various non- 

 olfactory systems from the betweenbrain (thalamus 

 and hypothalamus). 



In all fishes and amphibians the general plan of the 

 forebrain is as indicated very crudely in the accom- 

 panying diagram (Fig. 29), where a few only of the 

 chief afferent fiber systems are sketched in. In front 

 the olfactory nerve enters the olfactory bulb from the 

 peripheral sense organ. This primary olfactory center 

 is physiologically on the same plane as the sensory 

 terminal nuclei of the peripheral nerves of the me- 

 dulla oblongata and spinal cord. Farther back the 

 optic nerve similarly connects with the roof of the 

 midbrain, giving some collateral branches on the way 

 to the thalamus. Still farther back the remaining sen- 

 sory systems enter the medulla oblongata and spinal 

 cord. All of these primary sensory centers are con- 

 nected fore-and-aft in very intricate patterns by cor- 

 relating fibers (only a few of which are shown in 

 the diagram) of the sort already considered (p. 39). 



