Spinal Cord 25 



ducing immediate responses at the same level as that where 

 the stimulus is received. 



Those proprioceptive fibres which do not ascend to the 

 brain mostly end in connection with a group of cells near 

 the base of the dorsal column known as Clarke s column 

 {nucleus dorsalis), from which the secondary fibres pass to a 

 superficial position on the same side, where they ascend as 

 the dorsal and ventral spino-cerebellar tracts. This nucleus 

 is not clearly defined in the rat. 



The dorsal nerve root contains unmyelinated afferent 

 fibres, of w^hich the function is not known, but which may be 

 somatic. These, upon entering the cord, take up a position 

 superficial to the gelatinous substance of Rolando (PI. \'.), 

 where, along with a number of endogenous fibres, they form 

 a thin layer which may be detected in normal sections because 

 the large preponderance of unmyelinated fibres makes it 

 stain very lightly by the Weigert method and very deeply 

 by silver methods. This is the tract of Lissaiier {fasciculus 

 dor so-later alls). The fibres run a short distance up or down 

 the cord and finally end in the gelatinous substance of Rolando. 

 The greater part of the tract is located in the lateral funiculus 

 in the rat, where'there is an area just lateral to the gelatinous 

 substance which has the same structure as the thin band 

 superficial to the latter and which is continuous w^ith it. 



General Visceral Afferent System. 



The peripheral fibres of this system convey from the 

 visceral organs to the central nervous system impulses which 

 do not ordinarily affect consciousness, but which make 

 possible the nervous control of the functioning of these organs. 



They enter the spinal cord through the dorsal nerve root 

 along with the somatic afferent fibres and apparently end in 

 the ventro-lateral portion of the dorsal column. The im- 

 pulses may then be transmitted either to the visceral efferent 



