538 THE NERVOUS SYSTEM 



ramidal tract. As the size of this latter path diminishes with its 

 passage caudalward, the sulco- marginal fasciculus moves backward 

 along the anterior median sulcus into the position thus vacated. 

 In the thoracic and lumbar regions the tract under discussion occu- 

 pies the narrow area on either side of the anterior median fissure 

 which in the cervical region contains the direct pyramidal tract. 



The fibres of the fasciculus take origin in the anterior corpus 

 quadrigeminum of the opposite side, decussate through Meynert's 

 commissure, pass caudad in a position which is ventral to the aque- 

 duct of Sylvius and the posterior longitudinal fasciculus, and enter 

 the anterior column of the spinal cord. The bundle in passing 

 receives many neuraxes from the cells of Deiters* nucleus in the 

 rhombencephalon. The fibres derived from Deiters' nucleus, there- 

 fore, form a large portion of those which form this tract. The fas- 

 ciculus sulco-marginalis extends the entire length of the spinal 

 cord, its collaterals being probably distributed to the ventral horns. 



The ventral portion of this fasciculus also contains many ascend- 

 ing fibres which are thought to arise in the nerve cells of the dorsal 

 horns and intermediate zone of the opposite side. They then decus- 

 sate through the anterior commissure and pass cephalad either as 

 scattered fibres among those of the descending sulco-marginal fas- 

 ciculus or as a small bundle in the ventral margin of this tract. 

 These fibres form the ascending sulco-marginal fasciculus. 



The anterior ground bundle forms a large portion of the anterior 

 white columns. Like the lateral ground bundle, it connects neigh- 

 boring segments of the spinal cord and is similarly continued into 

 the medulla oblongata. In fact, the course of these two bundles is 

 so entirely comparable that they may be, and frequently are, col- 

 lectively described as the antero-lateral ground bundle. 



The formatio reticularis alba of the medulla oblongata receives, 

 among its many fibre bundles, certain fibres from the antero-lateral 

 ground bundles of the spinal cord which continue cephalad through 

 the reticular formation of the pons and midbrain for a varying dis- 

 tance. In the medulla and midbrain they are probably connected 

 with a small cell group which in each of these locations lies in or 

 near the median line : these are the superior and inferior central 

 nuclei. The ultimate destination of this group of fibres is, how- 

 ever, still obscure. 



The Posterior Longitudinal Fasciculus. Certain other fibres 

 from the antero-lateral ground bundles of the spinal cord, as they 

 enter the formatio reticularis of the medulla oblongata, unite to 



