THE MEDULLA OBLONG ATA. 



115 



How are the anterior pyramids made up ? 



The anterior columns of the cord send their fibres (the direct 

 pyramidal tract) up into the anterior pyramids, so that they are 

 continuous tracts. Other fibres from the lateral columns join the 

 fibres of the anterior pyramids, and here cross in bundles to the 

 opposite side. These fibres may be seen -crossing the anterior 

 fissure between the pyramids by gently separating the anterior 

 pyramids. This is known as the decussation of the pyramids. The 

 fibres which cross in this way belong in the cord to the portion of 

 the lateral column known as the crossed or lateral pyramidal tract. 



How are the fibres of the anterior pyramids distributed to the 



brain? 



Most of the fibres pass on through the pons Varolii to be dis- 

 tributed in the cortex of the brain. Some of the fibres help to 

 make up the fillet, and pass to the optic thalamus, while others 

 pass to the cerebellum. Fig. 32 shows these relations very sat- 

 isfactorily. 



FIG. 32. 



OPTIC .THALAMUJ 



POST. PYRA lD >,. 



XTO cent 



REBCLLUM. 



Diagram of the Course of the Fibres through the Medulla to the Brain. 



How does the lateral column of the cord communicate with the 



brain through the medulla? 



The lateral column of the cord is broken into three tracts in the 

 medulla : one, we have just seen, joins the anterior pyramid of the 

 opposite side by the decussation ; a second joins the restiform body 



