SPINAL COED AND NERVES 



289 



already said that the fibres of the dorsal columns are the direct 

 continuation of the dorsal roots, which originate in the cells of 

 the spinal ganglia. The fibres of the tract of Goll are small 

 in diameter, and many of them, instead of entering the grey 

 matter of the cord, run as far as the medulla oblongata, where 

 they terminate in a special nucleus of grey matter (nucleus of 

 the funiculus gracilis). The tract of 

 Burdach consists of larger fibres which 

 send numerous collaterals to the grey 

 matter, and penetrate into it after a longer 

 or shorter course, coming into intimate 

 relation with the cells of Clarke's column. 

 Both these tracts undergo ascending de- 

 generation after section or compression of 

 the cord, or severance of the dorsal roots. 

 Coil's tract, which is myelinated later, 

 contains the longer paths which arise 

 from the lumbo-sacral and lower thoracic 

 roots ; while Burdach's tract, for the most 

 part, consists of short intraspinal paths, 

 with longer fibres derived from the higher 

 thoracic and cervical roots, which do not 

 enter the tract of Coll, and terminate in 

 the nucleus of the funiculus cuneatus or 

 nucleus of Burdach in the bulb. Thus 

 the tw T o bundles of the dorsal column are 

 composed principally of exogenous fibres 

 or spino-cerebral paths of conduction, but 

 they also contain endogenous fibres or 

 intraspinal paths. 



(e) The endogenous intraspinal fibres 

 are represented mainly by the portions 

 of the white matter adjacent to the grey. 

 Such is probably the character of the zone FlG . 177 ._ AsC ending degeneration 

 of fine fibres which fills the area between of tract of GOII and ventro- 



lateral ascending bundle of 



the ventral and dorsal horns, termed by Gowers, after crushing the 

 Sherrington and Grltnbaum the lateral ^IVowerS lv 

 limiting layer (Fig. 178, I. n. 5). But a 



certain number of intraspinal fibres with a short course are inter- 

 spersed among the fibres of the crossed pyramidal tract. They 

 are distinguished from the latter by their earlier myelination, and 

 by the fact that they do not degenerate with them (Miinzer). 



The so-called ground bundle of the ventro- lateral column 

 occupies a sectional area that varies with the area of the grey 

 matter. Probably many of its fibres are interspinal and serve to 

 connect the grey matter of different segments of the cord. 



The ventral zone of the dorsal column consists of fibres whose 



VOL. Ill 



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