320 



THE NERVOUS SYSTEM 



part of the medulla oblongata the greater part of the tract crosses to the opposite 

 side of the spinal cord and is continued as the lateral corticospinal tract in the 

 lateral funiculus. The smaller part is continued directly into the ventral fu- 

 niculus of the same side, as the ventral corticospinal tract. The fibers of the 

 ventral tract cross the median plane a few at a time and terminate, as do those of 

 the lateral tract, directly or indirectly in synaptic relations with the primary 

 motor neurons within the anterior gray column (Fig. 239). The ventral tract 

 is not evident as a well-marked bundle below the level of the midthoracic region. 



Mesencephalon 



N.IV 



Pans 



Corticobulbar tract 



Medulla oblongata 



Ventral corticospinal tract 

 Lateral corticospinal tract 



Spinal cord 



Ventral root 

 Fig. 239. The corticobulbar and corticospinal tracts. 



It has long been known that in the higher mammals the lateral pyramidal tract, although 

 consisting predominatingly of crossed fibers, contains a few homolateral fibers also (Simpson, 

 1902), and according to the observations of Dejerine (1914) and other investigators this 

 holds true for man also. Dejerine speaks of these uncrossed fibers in the lateral corticospinal 

 tract as a third bundle arising out of the motor decussation, and calls it the "homolateral" 

 corticospinal fasciculus. A good account of this tract and of the superficially placed bundle 

 of uncrossed pyramidal fibers that is to be found in the ventral part of the lateral funiculus 

 in the cervical portion of the spinal cord is given by Barnes (1901). 



Neuron II. To the lower or primary motor neurons belong the large multi- 

 polar cells of the anterior gray column of the spinal cord. These give rise to the 

 motor fibers that leave the spinal cord through the ventral roots and are dis- 

 tributed through the spinal nerves to the skeletal musculature. 



The motor path for the cranial nerves is less well known. It includes the 

 corticobulbar tract and those fibers of the cranial nerves which innervate striated 

 musculature. 



Neuron I, or upper motor neuron. The corticobulbar fibers arise from the 



