288 MICROSCOPIC ANATOMY OF THE OEGAX*. 



and rotates partially, so that it becomes oblique. In the mid- 

 brain the pyramidal tract lies external and ventral to the 

 medial lenmiscus, but in passing upward the sensory tract 

 passes in front of the pyramidal tract, and the two bundles to- 

 gether make the internal capsule which lies just external to 

 the thalamus and is connected with the region of the cortex 

 around the fissure of Rolando. The form of the sensory tract 

 is emphasized, because all the other structures are related to it. 

 In the medulla it is the medial, vertical sheet ; opposite the 

 ventral part of it is the olive ; opposite the dorsal part of it 

 is the area of the formatio reticularis, which contains all the 

 nerves of the region. In the pons the sensory tract forms 

 a horizontal sheet. Ventral to it lie the pontal nuclei; while 

 dorsal to it lie the formatio reticularis and the nerves. 



In the midbrain the sensory tract is an oblique sheet. It 

 lies between the red nucleus and the formatio reticularis on 

 the inside, and the pyramidal tract on the outside. 



The pyramidal tracts start from the cerebral cortex around 

 the fissure of Rolando, and pass downward in the posterior part 

 of the internal capsule into the peduncle or rnidbrain. Here 

 the tract is a compact band of fibres external to the medial 

 lemniscus. It passes into the ventral part of the pons, where 

 it is broken into small bundles by the cells of the pontal nuclei. 

 In entering the medulla, these bundles collect into a tract 

 that passes to the cord just ventral to the interolivary bundle. 

 At the lower end of the medulla these fibres decussate in the 

 raplie. Part of them enter the ventral columns of the cord, 

 part cut through the ventral horn and enter the lateral col- 

 umns. In the brain -stem, fibres leave the pyramidal tract, 

 decussate in small bundles or as single fibres, and enter the 

 motor nuclei. 



Group 2, The cerebellum has three peduncles inferior, 

 middle, and superior. The inferior receives fibres from the 

 cord and the medulla. The direct cerebellar tract, which is a 

 narrow band on the surface of the cord, becomes a compact 

 bundle in entering the medulla, and receives a group of fibres 

 from the dorsal columns of the cord (Fig. 215). These fibres, 



