872 



THE NERVE SYSTEM 



Pyramidal Decussation (dccussatio pyramidurri). An important change in the 

 internal structure is caused by the passage of the fibres of the pyramidal tract as 

 these pass to the same and opposite sides of the cord, the latter category forming 



DORSAL 

 ROOTS 



DORSO-MEDIAN 

 FISSURE 



DORSAL 

 HORN 



DORSO-LATERAL 

 COLUMN 



DORSO-MEDIAN 



FISSURE 



NUCLEUS GRACILiS 

 SENSOR 

 ROOTS 



.CROSSED PYRAM- 

 IDAL TRACT 



VENTRALX 

 ROOTS 



VENTRO-MEDIAN 

 FISSURE 



VENTRO-MEDIAN 

 FISSURE 



FIG. 637. Transverse section of the medulla oblongata 

 at its lower end. (Testut.) 



FIG. 638. Transverse section of the medulla 

 oblongata at the decussation oi the pyramids, 

 (Testut, after Duval.) 



LATERAL 

 LEMNISCUS 



TRAPEZIUM 



MEDIAL 

 LEMNISCUS 



DECUSSATION 

 OF LEMNISCT 



POSTERIOR 



QUADRIGEMINAL 



BODY 



NUCLEUS OF 

 LATERAL LEMNISCUS 



VENTRAL 



COCHLEAR NUCLEUS 



TERMINAL NUCLEI 



AFFERENT 

 CRANIAL NERVES 



NUCLEUS OF 

 F. GRACILIS 



NUCLEUS OF 

 F. CUNEATUS 



FIG. 639. Diagram showing the course of the lemnis'ci (fillets) and their decussation. 



