534 ELEMENTARY PHYSIOLOGY 



When this tract is traced forwards above the bulb it is 

 found to pass into the cms cerebri of its own side and to 

 pass along the lower or ventral part of the crus, which is 

 known as the pes. The optic thalami and corpora striata 

 are, as we have seen (p. 508), deposits on the course of 

 the crura as the latter sweep forward into the hemispheres. 

 Now when tlie fibres of the pyramidal tract reach the level 

 of the thalamus they rise up out of the cms, and, spread- 

 ing like a fan, pass posteriorly between the optic thalamus 

 and the hinder end of the corpus striatum, and anteriorly 

 between the two parts of wliich the front end of the corpus 

 striatum is composed. The fibres of the pyramidal tract 

 as they thus pass between the optic thalamus and corpus 

 striatum are known as the internal capsule, and the 

 bend the fibres make as they rise out of the crus is known 

 as its "knee." From this point onwards the fibres pass 

 directly to their connections with the cells in the grey 

 matter of the cortex along the region of the fissure of 

 Rolando. The preceding Figure 172 shows diagrammatic- 

 ally the course of the pyramidal tract from the cerebral 

 cortex to the spinal cord. 



