ROOTS OF THE SPINAL NERVES. 365 



sure, to the center and columnae of the opposite crescent. These 

 fibers end in relation with the dendrites or cell-bodies situated in 

 those several regions of the crescent at various levels: (a) At the 

 same level as the nerve, (b) at a lower level than the nerve, through 

 the descending radicular tracts, and (c) at a higher level, through 

 the collaterals given off by the ascending tracts. (2) The large 

 ascending T-branches of the inner set of fibers run to the me- 

 dulla oblongata. They form the fasciculus gracilis and fasciculus 

 cuneatus and ascend to the nuclei of those columns in the medulla 

 oblongata. They terminate in the nuclei funiculi gracilis and cu- 

 neati. Hence the terminal nuclei (nn. terminales) of any spinal 

 nerve are composed of the gray crescents of the cord, chiefly at 

 the same level, and of the nucleus funiculi gracilis or the nucleus 

 funiculi cuneati in the medulla. 



Physiologically, we may divide the fibers of the posterior 

 roots of the spinal nerves into four groups, viz.: i. Excito-reflex 

 fibers which terminate in all parts of both crescents. 2. Fibers 

 bearing impulses of the muscular and tactile senses from muscles, 

 tendons, joints and skin, through the ^posterior column, to the nu- 

 cleus funiculi gracilis and nucleus funiculi cuneati. 3. Fibers 

 carrying impulses of the muscular sense from the viscera to the 

 dorsal nucleus. 4. Fibers transmitting pain, temperature and 

 tactile impulses to that part of the same and opposite crescent 

 whence the spino-thalamic and ascending anterior cerebello-spinal 

 tracts take their origin. 



Lesions. The posterior roots of the spinal nerves and the spinal 

 ganglia are affected in locomotor ataxia, and the lesion extends 

 to the marginal tract (of Lissauer) and the posterior column of the 

 cord. Excepting the fasciculus proprius, the whole posterior 

 column becomes involved. 



