THE ASSOCIATION PATHS 537 



taining association fibres which connect the posterior horn cells of 

 adjacent levels. This tract is most prominent in the cervical region. 

 It is absent from the lower portions of the spinal cord. 



The posterior white column in the sacral region of the spinal 

 cord contains a small bundle which, with its fellow of the opposite 

 side, forms an oval or cuneate area which incloses the posterior 

 median septum. This short tract is the fasciculus dorso-medialis 

 (dor so-medial sacral bundle, triangle median, Flechsig's oval field). 

 Though part of its fibres are thought to come from the dorsal roots 

 and are therefore exogenous, yet many are undoubtedly derived 

 from the more cephalad regions of the spinal cord. This fascicu- 

 lus is therefore homologous with those fibres which at higher levels 

 are found in the comma tract. 



In the lateral white column are four distinct tracts, the inter- 

 medio-lateral fasciculus, the lateral border zone, the lateral ground 

 bundle, and Helwig's fasciculus. 



The intermedio-lateral fasciculus (rubro-spinal tract, von Mona- 

 kow's bundle) occupies a small area at the ventral margin of the 

 crossed pyramidal tract. The fibres of this bundle probably arise 

 in the optic thalamus and red nucleus of the opposite side. They 

 decussate in the tegmentum and reach the spinal cord through the 

 formatio reticularis of the pons and medulla. The fasciculus ex- 

 tends the entire length of the spinal cord, its collaterals being 

 distributed to the ventral horns. 



The lateral border zone is a thin area adjoining the lateral sur- 

 face of the grey matter of the spinal cord. Its short fibres connect 

 the nerve cells of neighboring spinal segments. 



The lateral ground bundle includes many fibres, some ascending 

 and some descending, which connect more distant segments of the 

 spinal cord, and in the medulla oblongata blend with the anterior 

 ground bundle to enter the formatio reticularis alba and posterior 

 longitudinal fasciculus. 



Helwig's fasciculus is a short tract, found only in the cervical 

 region. It is triangular, or at times crescentic in section, and lies 

 in front of the broad apices of the ventral horns at the ventral 

 margin of the lateral white columns. The origin and destination 

 of these fibres is not yet known. 



The anterior white column contains the sulco-marginal fasciculi 

 and an anterior or ventral ground bundle. 



The descending sulco-marginal fasciculus (Lowenthal's tract) in 

 the cervical region occupies an area just ventral to the direct py- 



