THE BRAIX OR ENCEPHALOX 



861 



The plan of structure of the brain differs, therefore, from the comparatively 

 simple arrangement of the gray and white .substance in the spinal cord. In the 

 brain the gray substance is not centrally situated throughout, and there is a tendency 

 to nuclear differentiation of greaf and small ganglionic masses. These are con- 

 nected with each other and with the centres in the cord by longitudinal strands 

 of fibres of greater and less length, as well as by transverse associating fibres 



FASC. 

 SOLITARIUS 



VAGUS 

 GANGLION 



NJOI 



B 



.PRIMARY I RHOMBOIDAL 



SECONDARY ) LIP 



FASC 

 SOLITARIUS 



OMBOIDAL LIP 

 (FUSED) 



FASC. SOLITARIUS 



FIG. 629. Three stages in the development of the medulla oblongata, showing the metamorphosis of 

 the rhomboidal lip. (Modified after His.) 



uniting the bilateral nuclei of the same ganglionic category; with the periphery 

 they gain connection through the cranial nerves and (via the spinal cord) the 

 spinal nerves. 



In tracing the various structures of the brain from the medulla oblongata to the 

 cerebral cortex we follow anatomically what nature has done in the evolution 

 of the highest type of brain from that of the simplest and most ancient vertebrate. 

 In the medulla oblongata lie the centres which exert a very direct influence over 

 those of the entire cord. The striate bodies and the thalami form a connecting 

 link between the higher cerebral cortex and the medulla oblongata and cord below. 

 The extensive cerebral cortex, an aggregation of psychic centres and therefore 

 the seat of the will, controls the activities of the fore-brain ganglia (corpus striatum, 

 thalamus) and the cerebellar cortex, and these in turn preside over the functions 



