



ESSENTIALS OF PHYSIOLOGY. 



THE DESCENDING TRACTS (OE FASCICULI). 



The principal long descending tracts are the direct and crossed 

 pyramidal tracts (the anterior and lateral cerebro-spinal fasciculi), both 

 of which take origin in the cerebral hemisphere. The pre-central con- 

 volution on each side contains certain large pyramidal cells, known as 

 Betz cells, the axons of which unite to form a tract which runs through 



Posterior median sulcus. 

 Cornu-commissural fasciculus. 

 Funiculus gracilis. 



Comma tract. 

 Funiculus cuneatus. 



Lissauer'p 

 bundle 



Posterior 

 nerve roots. 



\ Anterior 

 nerve roots. 



Superficial antero-lateral tract. . 



Olivo-spinal tract. 



Relay fibres. 



Direct pyramidal tract. 

 Anterior median fissure. 



FIG. 10. Diagram of the principal tracts in the spinal cord. (Gray's Anatomy.} 



the mid-brain and pons to the medulla oblongata. In the latter 

 structure the majority of the fibres in each tract cross to the opposite 

 side to become the crossed pyramidal tract (lateral cerebro-spinal 

 fasciculus) of the spinal cord, while the remaining fibres run down with- 

 out crossing to become the direct pyramidal tract (anterior cerebro- 

 spinal fasciculus) of the same side. Some of the uncrossed fibres, how- 

 ever, join the crossed pyramidal tract wjiich has crossed from the 

 opposite 'side. 



The fibres of the crossed pyramidal tract terminate by running into 



