THE NERVOUS SYSTEM. 817 



umns, while the columns of Clarke show a diminution in the number of 

 delicate fibrils which normally surround the ganglion cells. 



Changes have also been described in the spinal root of the fifth cranial 

 nerve and in the fasciculus solitarius which consists of afferent fibres of 



FIG. 534. POSTERIOR SPINAL SCLEROSIS. (TABES DORSALIS.) 



A portion of sclerosed area in the posterior columns of the spinal cord, a. New-formed connective tissue ; 

 h, blood-vessels ; c, nerve fibres ; d, atrophied nerve fibres. 



the vagus and glosso-pharyngeal nerves. These fibres are analogous to 

 those of the posterior columns and the changes in them are similar. 



Degenerations of a secondary character may occur in those systems 

 of neurones which are more or less dependent upon the peripheral sen- 

 sory neurone system for their impulses. Thus the cells of Clarke's col- 

 umn may be affected, with resulting degeneration of their axoues which 

 make up the direct cerebellar tract. This degeneration extends through 

 the restiform body to the termination of the tract in the cerebellum. 

 The cells of the gray matter whose axoues form Gowers' tract may be 

 degenerated, with consequent degeneration of the fibres of this tract, 

 lu the medulla the cells of the nucleus gracilis and nucleus cuneatus 

 may be affected, thus determining an ascending degeneration along the 

 tracts followed by their axoues. Similar in character is the degeneration 

 of the cells of the anterior horns noted by Condoleon. These changes in 

 the anterior-horn cells have been accepted by some investigators as ex- 

 planatory of the various trophic disturbances which so frequently occur 

 during the course of tabes. Similar changes have been found in the 

 nuclei of two of the motor cranial nerves, the oculomotor and the hypo- 

 glossal. Others ascribe the trophic disturbances to a peripheral neuritis. 

 Marie ' describes a case interesting in this connection, in which there was 

 marked herniatrophy of the tongue with distinct changes in both main 

 and accessory nuclei of the hypoglossal nerve on the same side, the oppo- 



1 Marie, loc. cit., p. 258. 

 52 



