THE SPINAL CORD AS A CONDUCTOR 353 



as the lower end of the cord. They end in the spinal cord by turning into the 

 grey matter where they break up into a fine bunch of fibrils in close con- 

 nection with the motor cells of the anterior horn, or, according to Schafer 

 with the cells of the posterior horn. 



On their way down the cord they give off fin* side branches or collaterals 

 which run into the grey matter, thus establishing connections between one 

 cortical cell and the anterior cornual cells of several different segments of 

 the spinal cord. These fibres carry voluntary motor impulses from the 

 cerebral cortex to the reflex motor mechanisms of the cord. Their destiuc- 

 tion by disease, or otherwise, causes the abolition of voluntary control over 

 the muscles, without, however, 

 interfering with the reflex motor 

 functions of the cord, which, as a 

 matter of fact, are increased in 

 cases where these tracts have un- 

 dergone degeneration. 



(2) RUBRO-SPINAL OR 

 PREPYRAMIDAL TRACT (also 

 called Monakow's Bundle). This 

 is a fairly compact group of 

 fibres which degenerate down- 

 wards after section of the cord. 

 It is situated, in cross- section, FIG. 174. Diagram (from SCHAFER) showing the 

 ventral to the pyramidal tracts. ascending (right side) and the descending (left 



side) tracts in the spinal cord. 

 1, crossed pyramidal ; 2, direct pyramidal ; 

 the Cells in the red nucleus, a 3, antero-lateral descending: 3a, spine-olivary 

 ,. ., ., descending (bundle of Helweg) ; 4, pre-pyramidal 



mass of grey matter in the mid- (rub ro-spinal) ; 5, comma; 6, postero mesial ; 



the 1' postero -lateral; 8, Lissauer's tract; 9, dorsal 

 (ascending) cerebellar ; 10, antero-lateral ascend- 

 ing ; sm, septo- marginal ; spl, dorsal root zone ; 



(3)VESTIBUL O-S P I N AL a ' anterior horn-cells ; t, intermedia-lateral horn ; 



p, cells of posterior horn; d, Clarke's column. 

 The fine dots represent the situation of the 

 ' internuncial ' or ' endogenous ' fibres of the spinal 

 cord. 



Its fibres can be traced 



brain lying ventrally to 

 nucleus of the third nerve. 



TRACT. This consists of scat- 

 tered fibres in the antero-lateral 

 column, which degenerate in the 

 downward direction. They were formerly supposed to be derived from 

 the cerebellum of the same side, but it has been shown that they are 

 in all probability derived from Deiters' nucleus in the medulla an 

 important transmitting station between the cerebellum and cord. 



(4) OLIVO-SPINAL AND THALAMICO-SPINAL TRACTS (Bundle of 

 Helweg). This tract is also situated in the antero-lateral column, opposite 

 the head of the anterior horn. It consists mainly of fibres which pass from 

 the thalamus (the fore brain) through the inferior olive of the medulla down- 

 wards in the cord as far as the lower cervical region. 



(5) COMMA TRACT. This tract lies in the posterior columns at the 

 junction of the postero-median and postero -lateral portions. It consists 

 for the most part of the descending branches of the afferent dorsal nerve- 

 roots which enter the cord. These divide as they enter the cord, and their 



