x SPINAL AND CEREBRAL NERVES 163 



Each sympathetic nerve has altogether nine or ten 

 ganglia, each connected with one of the spinal nerves, 

 and from the ganglia branches are given off which 

 supply the heart and blood-vessels, the stomach, in- 

 testine, liver, kidneys, reproductive organs, and urinary 

 bladder. 



Origin of the Spinal Nerves. The mode of origin of 

 the nerves from the spinal cord is peculiar and character- 

 istic. Traced, towards the cord, each nerve is found, on 

 reaching the intervertebral foramen from which it 



FIG. 52. Transverse section through the vertebral column and spinal cord of the 



Frog, to show the mode of origin of the spinal nerves. ( X 6.) 

 c. c. central canal ; en, centrum with periosteum ; d. f. dorsal fissure ; d. m. 

 dura mater ; d, r. dorsal root ; g. m. grey matter ; gn. ganglion of dorsal root ; 

 n. a. neural arch ; n. sp. neural spine ; p. m. pia mater ; t, nerve trunk with its 

 sheath (ventral branch) : t'. dorsal branch : Tr. pr. transverse process ; v. f. 

 * " ' " ' " c Howes.) 





ventral fissure ; v, r. ventral root ; w. m, white matter. (After Howes.) 



emerges, to divide into two a dorsal root which springs 

 from the dorsal, and a ventral root which arises from 

 the ventral region of the cord (Fig. 52, d.r, v.r). The 

 dorsal root is distinguished from the ventral by being 

 dilated into a. ganglion (gn). In Fig. 51 these ganglia lie 

 hidden within certain calcareous bodies (C) in this region. 



Cerebral Nerves. There are ten pairs of cerebral 

 nerves, some of which are purely sensory, some purely 

 motor, some mixed. 



The first or olfactory nerves (Fig. 49, /) arise from the 

 olfactory lobes, and pass through two holes in the trans- 



