THE MESEKCEPHALON 



501 



On the dorsal aspect of the mesencephalon, just cephalad from 

 the decussation of the fourth pair of nerves, are the inferior corpora 

 quadrigemina (inferior colliculi). Transections at this level show 

 a large oval grey mass, corresponding to the prominence on either 

 side. These are the nuclei of the inferior corpora quadrigemina. 



FIG. 389. A SECTION OF THE HUMAN BRAIN STEM, AT THE LEVEL OF THE POSTERIOR 



CORPORA QUADRIGEMINA. 



Aq, aqueductus Fallopii; Brqp, peduncle of the posterior corpora quadrigemina, 

 cH, central tract of the tegmentum ; Coqp, commissure of the posterior corpora quadri- 

 gemina ; Cpbg, parabigeminal body ; DBrcjd, dorsal, and DBrcjv, ventral portion of the 

 decussation of the brachium conjunctivum; Fcoea, anterior perforated space \fFp, fron- 

 tal pontine tract; Flp, posterior longitudinal bundle ; Fpl, lateral pontine bundle ; Fprd, 

 predorsal bundle ; fr, straight fibres of the midbrain ; fTp, temporo-pontine tract ; Glp, 

 globus pallidus of the lenticular nucleus; Gml, lateral ganglion of the midbrain ; Hg, 

 central grey matter; IH, lateral bundle of the tegmentum ; Lmp, bundle from the lem- 

 niscus to the crusta; Ndtg\ accessory dorsal tegmental nucleus; NIV, nucleus of the 

 trochlearis ; NlAq, lateral nucleus of the aqueduct ; NQp, nucleus of the posterior cor- 

 pora quadrigemina ; pern, peduncle of the mammillary body ; Po, pons ; Ppbg, parabi- 

 geminal fibres ; prP, propons ; Py, pyramid ; Spp, posterior perforated space ; SnS, sub- 

 stantia nigra ; Srt, substantia reticularis alba ; Stri, intermediate layer ; 7Vs,rubro-spinal 

 tract; Tst, spino-tectal and thalamic tract; Vc, cerebral, and F, crossed root of the 

 trigeminus. Weigert's stain, x 3i. (After Marburg.) 



