322 THE VITAL FUNCTIONS. 



Although we are entirely ignorant of the nature 

 of the nervous power, we know that, when em- 

 ployed in the vital functions, it acts through the 

 medium of a particular set of fibres, which form 

 part of the nervous system, and are classed, there- 

 fore, among the nerves. The principal filaments 

 of this class of nerves compose what is called the 

 sympathetic nerve, from its being regarded as the 

 medium of extensive sympathies among the organs ; 

 but the whole assemblage of these nerves is more 

 commonly known by the name of the ganglionic 

 system, from the circumstance of their being con- 

 nected with small masses of nervous substance, 

 termed ganglia, which are placed in different parts 

 of their course. Fig. 379, represents a ganglion (g), 

 at which numerous filaments of nerves are collected ; 

 some entering into the ganglion, and others passing- 

 out of it, and afterwards divided into smaller fila- 

 ments F and B. Within the ganglion, there is 

 always found a mass, more or less considerable, of 

 a substance apparently similar to the soft exterior, 

 or cortical portion of the brain : or, as it has also 

 been termed of grey neurine. The nervous filaments 

 Avhich are connected with this substance may be 

 distinguished into the afferent nerves, or those which 

 convey impressions arising at a distant, or peri- 

 phral part, to the central neurine ; and the efferent 

 nerves, or tliose which transfer impressions from 

 these centres to remoter parts, whether those 

 parts be muscular fibres, blood-vessels, or secreting 

 organs. 



The ganglia of the sympathetic nerve are con- 

 nected by nervous filaments with every part of the 

 brain and spinal cord, the great central organs of 

 the nervous system ; and they also send out innu- 



