DIVISIONS OF THE NERVOUS SUBSTANCE. 549 



Functional Divisions of the Nervous Substance. 



— The student who wishes to form for himself a comprehen- 

 sive and philosophical knowledge of the structure and func- 

 tions of nervous matter, will do well to examine it in its 

 simplest state of development as it is found in the radiated or 

 star-shaped animals, in which unequivocal voluntary locomo- 

 tive power exists, and where it is found dissected and simpli- 

 fied as it were by the hand of nature. In these animals we 

 find a ring of nervous ganglia, connected by intermediate cords 

 or commissures which unite them together, surrounding the 

 mouth and oesophagus ; and from the little nodules or ganglia 

 which are placed opposite the rays or limbs of the animal, part 

 nervous cords, which are distributed to the muscles, and are 

 unquestionably the instruments of locomotion. Proceeding 

 in his investigations up through the articulated, molluscous, 

 and vertebrated animals to man, he will find the nervous sys- 

 tem expanded in form, and complicated in arrangement, so as 

 to harmonize exactly with the development of the different 

 classes of animals, and the elevation of their vital functions. 

 Life, which appeared at the zero point of the scale, to be 

 manifested chiefly by motions excited by the contact of bodies, 

 (mere excito-motory phenomena,) becomes complicated as we 

 ascend, with the presence of other functions, larger ganglia 

 being placed at the region of the head, which give the instinc- 

 tive impulses to the animal. As we proceed upwards towards 

 man, we find a cerebral ganglion, assuming more and more 

 the appearance of a brain, and endowed with instinctive 

 faculties, which approach slightly in character to the moral 

 and intellectual. Finally, in man himself we find this part 



