81(> THE NERVOUS SYSTEM. 



the cord below the affected region is normal, while above is the lesion of 

 an ascending degeneration. The lesion may in any case be asymmetrical, 

 one root of a segment being affected while the other remains normal. 

 Marie describes a variety of tabes in which the lesions begin in the 

 cranial nerves. 



In cases of advanced tabes (Fig. 533) there are often almost no nor- 

 mal nerve fibres in the posterior columns, the columns of Goll, of Bur- 

 dach, and of Lissaner presenting little but dense fibrous tissue. The 

 posterior fissure may be completely obliterated. There usually remain, 

 however, even in advanced tabes, undegenerated fibres bordering the pos- 



rjp 



FIG. 533. TABES DORSALIS. 

 Cervical region, showing an advanced stage of the lesion. 



terior commissure and the adjacent parts of the posterior horns. The 

 median area of Flechsig also remains intact. As already noted, these 

 fibres are endogenous. 



The microscopical appearance of the degenerated areas varies with the 

 stage of vhe process (Fig. 534). The new connective tissue may be at 

 first quite cellular; later the fibrillar elements predominate and the 

 tissue becomes dense and firm. Of the nerve fibres some have disap- 

 peared, others show degeneration of their medullary sheaths and axis 

 cylinders. Some few normal fibres are usually present even in advanced 

 sclerosis. The blood-vessels often have thickened walls. There may be 

 corpora amylacea and fat globules, the latter either free or collected in 

 cells. 



The lesion of tabes is not, however, confined to the posterior columns. 

 The fibres of these columns are constantly sending collaterals and termi- 

 nals into the gray matter. Most of these pass into the posterior horns, 

 an especially well-marked group entering Clarke's cell column. The 

 posterior horns are therefore usually smaller than normal, with a marked 

 reduction in the number of fibres entering them from the posterior col- 



