6C4 



A TEXTBOOK OF PHYSIOLOGY 



of the brachial and lumbar plexuses. In these enlargements the cord 

 is more or less oval in section ; in other parts it is nearly round. Down 

 the centre there runs a fine canal lined by ciliated epithelium, while 



post root gang. 



spongio-bt. 



germ, cells 



middle zone 

 mner zone 



ant root 



FIG. 380. DIAGRAMMATIC SECTION SHOWING THE THREE ZONES OF THE SPINAL. 

 NEURAL TUBE AT THE SIXTH WEEK. (Keith.) 



post mes. (from post roots/ 



post fat (from post roots) 

 ^margin, (from post rooty) 



crossed pyram. (from 

 "motor cortex) 



-asc. cerebellaf 



outer zone 

 middle zone. 



inner zone 



asc. cerebellar 



desc. cerebellar (fror.i 

 cerebellum) 



ant pyram (from motor cortex) 



FIG. 390. DIAGRAMMATIC SECTION OF SPINAL CORD TO SHOW THE PARTS FORMED IN 

 THE THREK ZONES OF THE EMBRYONIC SPINAL CORD. (Keith.) 



two fissures in the middle line dip into the cord anteriorly and pos- 

 teriorly. The anterior fissure is more or less open a kind of furrow 

 the posterior fissure is practically closed, being formed mainly of 

 supporting neuroglial tissue. 



On section, the spinal cord is seen to be composed of white and 

 grey matter. The latter is centrally placed in the shape of an H . 

 The joining limb of the H passes on either side of the central canal 



