NERVOUS SYSTEM. 245 



ascending fibres from the periphery of the cerebral mass, and 

 as forming the posterior or sensitive columns of the spinal 

 chord by their descent from the brain, are larger than in the 

 lower orders of quadrupeds. The periphery of the whole 

 body is now the most largely supplied with symmetrical 

 nerves of motion and sensation, whose roots are the most 

 imbedded and approximated ; the great central columns of 

 these nerves are the most intimately and compactly united 

 to each other in every part of the axis, and in passing from 

 the embryo state to this most complicated condition, the 

 great spino-cerebral axis of man presents successively the 

 various conditions exhibited as adult forms in the lower 

 classes of animals. The great sympathetic also presents its 

 highest condition of development in quadrupeds and man, 

 being here most intimately united with all the spinal and 

 cranial nerves from the caudal extremity of the trunk to the 

 trigemini, or fifth pair of cranial nerves. It forms numerous 

 distinct cineritious ganglia in the head, on both sides of the 

 neck, along the two sides of the vertebral column, and in 

 the three great cavities of the trunk, the thorax, the abdomen, 

 and the pelvis, embracing with its large anastomos- 

 ing plexuses and ganglia the great arteries proceeding 

 to the viscera, and; thus it establishes in the most com- 

 plicated of animal forms the greatest unity of action and 

 mutual dependence of all the organs of animal and of vege- 

 tative life. 



