TRACTS OF THE SPINAL CORD. 355 



strand is the medial panto-spinal tract (Collieri). It rises from 

 all the nuclei of the reticular formation but chiefly from the nu- 

 clei centrales and the nucleus lateralis medius in the pons. Form- 

 ing a part of the medial longitudinal bundle of the same side, 

 its fibers end in the center of the crescent as it descends the cord. 

 Within the lateral fasciculus proprius, descends the lateral ponto- 

 spinal tract (Collieri). This tract has the same origin and termina- 

 tion as the medial ponto-spinal tract except that it decussates. It 

 crosses near its origin right through the medial longitudinal bundles. 

 Both ponto-spinal tracts extend to the lower part of the cord. 



The anterior pyramidal tract (fasciculus cerebro-spinalis 

 anterior), occupies a thin area next the anterior median fissure 

 (Figs. 1 02 and 103). It is the direct continuation of about 10 per 

 cent, of the pyramidal tract in the medulla. Its fibers are axones 

 of cortical cells whose bodies are situated in the anterior central 

 gyrus of the cerebrum. As the tract descends in the cord, the 

 fibers decussate through the white anterior commissure, and ter- 

 minate in relation with the cells of the opposite gray crescent, prob- 

 ably, in the posterior columna. It reaches to the fifth sacral 

 segment (Collier). Imbedded in the anterior pyramidal tract 

 is a small strand first described by Held, the anterior longitudinal 

 bundle. 



Anterior Longitudinal Bundle (Figs. 102 and 103). Held called 

 it the fasciculus longitudinalis ventralis. It occupies a very nar- 

 row strip in the anterior column just beside the entrance of the 

 anterior median fissure. The anterior longitudinal bundle has 

 already been traced from its origin in the superior quadrigeminal 

 colliculus, through the dorsal tegmented decussation (Meynerti) 

 to a position in the mid-brain ventro-lateral from the medial 

 longitudinal bundle. It descends in that relative position through 

 the pons and half the medulla; near the pyramidal decussation 

 the anterior and medial longitudinal bundles are brought together 

 and lie between that decussation and the isolated head of the an- 

 terior columna; they diverge upon entering the cord and remain 

 separate to the end. The anterior longitudinal bundle ends in 

 both anterior columnae (Collier). It forms the middle link in 

 the ocular and pupillary reflex arcs. 



