THE DIENCEPHALON 



503 



leaving a deep but broad sulcus in the median line, in the floor 

 of which is the posterior perforated space. The root bundles of 

 the third cranial nerves pass ventral ward from their nuclei of 



FIG. 390. A SECTION OF THE HUMAN BRAIN STEM, AT THE LEVEL OF THE POSTERIOR 



BORDER OF THE RED NUCLEUS. 



Cgl, lateral geniculate body ; Cgm, mesial geniculate body ; Girl, internal capsule ; 

 Cop, posterior commissure; EW, Edinger-Westphal nucleus; Fcop, fasciculus of the 

 posterior commissure ; Fe Qa, efferent fibres from the roof of the mesencephalon ; Ftp, 

 posterior longitudinal bundle ; fp, perforating fibres of the crusta ; frtf. fasciculus retro- 

 tiexus of Meynert ; Glp, pineal gland ; H, Forel's field ; ///, oculomotor nerve ; LM, 

 Wernicke's field ; Nc, caudate nucleus ; Ncop, nucleus of the posterior commissure ; NQa, 

 nucleus of the superior corpora quadrigemina; Mg, red nucleus; Pcm, peduncle of the 

 mammillary body : Pp, crusta ; Pal, pulvinar ; 8n&, substantia nigra ; Stri, intermediate 

 layer; 777, optic tract; Tpt, transverse tract of the peduncle; Tst, spino-tectal and 

 thalamic tract. Weigert's stain, x Ij. (After Marburg.) 



origin, penetrate the region of the red nuclei, and emerge through 

 the posterior perforated space at the mesial border of the crura 

 cerebri. 



THE DIENCEPHALON, With the next step cerebralward the 

 aqueduct of Sylvius opens into the third ventricle and the mesen- 

 cephalic nuclei are replaced by the large basal nuclei of the cere- 

 brum. This group of nuclei include the optic thalamus, caudate 

 nucleus, lenticular nucleus, hypothalmic nucleus, and the nucleus of 

 the posterior longitudinal fasciculus (Darkschewitsch's nucleus). 



The nucleus of the posterior longitudinal fasciculus (Darksche- 

 witscli) lies on either side of the median line, ventral and some- 

 what cephalad from the oculo-motor nuclei. In it the posterior 

 longitudinal fasciculus, in part, at least, terminates. 



