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HUMAN PHYSIOLOGY 



active, and get their medullary sheath later than the fibres 

 of ingoing tracts. The crossed and direct pyramidal tracts 

 are non-medullated at birth, while the ingoing tracts are 

 medullated. 



nc- 



cyen 



-pern. 



Fio. 82. View from above of the medulla oblongata, corpora quadri- 

 gemina, and optic thalami. c.l.a., posterior columns of cord ; 

 VIII., XII., JT., indicate the nuclei of these cranial nerves 

 in the floor of the fourth ventricle ; p.c.i. , the restiform body ; 

 p.c.m., the middle peduncle of the cerebellum; p.c.s., the 

 superior peduncle of the cerebellum; t.q., the anterior and 

 posterior corpora quadrigemina ; c.o. , the optic thalamus with 

 pulvinar (pulv.) and external and internal geniculate bodies 

 behind it ; e.p., the pineal body. (VAN GEHUCHTEN.) 



B. THE MEDULLA OBLONGATA. 

 1. Structure. 



The medulla oblongata may be regarded as the upper end 

 of the spinal cord, and it connects that structure with the 

 brain (Fig. 82). The cord expands and the posterior mesial 



