CONDUCTING PATHWAYS IN THE SPINAL CORD 593 



ventrolatcral cerebellar tract or Gowers's bundle; in front of the pons they 

 bend around and enter the cerebellum by way of the superior peduncle. (3) 

 Fibers which originate in the cells of Clarke's column pass forward to the 

 cerebellum. Some of these are scattered among the fibers of other tracts, but 

 part of them also form a compact bundle (Flechsig's bundle), which, from its 

 position in the cord, is described as the dorsolateral cerebellar tract. All these 

 fibers pass through the inferior peduncle and can be traced to the superior 

 vermis of the cerebellum. 



The anterior roots are for the most part connected with nerve cells of the 

 anterior horn on the same side; a few anterior root fibers spring from cells 

 of the opposite side. 



Secondary efferent pathways descend from the cerebral cortex to these 

 cells, forming the so-called pyramidal tracts (or the cortico-spinal tract). 

 Their mode of connection with the anterior horn cells, however, has not been 

 definitely made out. In the medulla most of these fibers cross (pyramidal 

 crossing) and continue downward in what is known as the lateral or crossed 

 pyramidal tract, which gives off collaterals to the motor cells of the same side. 

 A varying number of pyramidal fibers, however, do not take part in this 

 crossing of the pyramid, but descend in the anterior or direct pyramidal 

 tract, also to a less extent in the lateral pyramidal tract. During their down- 

 ward course these direct tracts are all the while giving off fibers, most of them 

 collaterals, to the opposite side of the spinal cord, so that the crossing of the 

 cortico-spinal fibers becomes more and more complete the farther we proceed 

 caudalward. The result is that the anterior pyramidal tracts can be followed 

 only to about the middle of the thoracic cord, or, exceptionally, to the lumbar 

 cord. But fibers of the direct pyramidal tract are also connected with anterior 

 horn cells of the same side. 



Ventral to the crossed pyramidal tract there runs another bundle of long 

 fibers, namely, the rubro-spinal tract or Monalcow's bundle, arising in the red 

 nucleus of the tegmentum and sending fibers to the opposite side of the cord. 

 Other long-fibered efferent tracts are the tecto-spinal and the vestibulo-spinal. 

 The former arises in the roof of the mesencephalon and runs, as a crossed 

 tract in the anterior column of the spinal cord, and as an uncrossed tract in 

 the lateral columns. The latter springs from Deiter's nucleus in the medulla 

 oblongata, where some of the vestibular nerve fibers have a terminal station, 

 and is found in the anterior columns of the cord. 



The tracts thus far described G oil's and Burdach's columns, the dorso- 

 and ventrolateral cerebellar tracts, the pyramidal tracts and the efferent tracts 

 just mentioned all represent connecting pathways between distant portions 

 of the central nervous system. Flateau has drawn attention to the fact that 

 they tend to occupy the border zone of the white columns in the cord; that 

 while they may at certain levels be displaced from this zone, they always 

 return to it at the first opportunity and thereafter keep their position until 

 they turn- into the gray matter. 



The inner zones of the white columns are occupied in the main by short- 

 fibered tracts connecting different levels of the cord. Some of these tracts 

 arise from widely distributed multipolar cells (column cells), which send axis 

 cylinders into the antero-lateral column of the same or of the opposite side. 



