342 



NERVOUS SYSTEM. 



In this portion of the brain the continuation of the central 

 cavity is a narrow canal which receives the name cerebral 

 aqueduct (aqueductus cerebri) or aqueduct of Sylvius. 



J 



-a 



-n 



FIG. 138. VENTRAL SURFACE OF THE BRAIN. 



I- XII, the twelve cranial nerves in order; /, olfactory bulb; //, N. opticus; ///. 

 N. oculomotorius; IV, N. trochlearis; V, N. trigeminus (I, mandibular nerve; 2, 

 maxillary nerve; 3, ophthalmic nerve; 4, sensory root); VI. N. abducens; VII, N. 

 facialis; VIII, N. acusticus; IX, N. glossopharyngeus; X, N. vagus; XI, N. acces- 

 sorius; XII, N. hypoglossus. a, tractus olfactorius; b, substantia perforata anterior; 

 c, optic chiasma; d, infundibulum ; e, hypophysis; f, lobus pyriformis, or tractus 

 postrhinalis; g. pedunculi cerebri; h, substantia perforata posterior; i, pons; /, sulcus 

 basilaris of pons; k, semilunar (or Gasserian) ganglion; /, trapezium; m, area ovalis; 

 n, area elliptica; o, pyramidal tracts; /, anterior or ventral fissure; q, foramen 

 caecum; r, anterior lateral sulcus; s, first cervical nerve. 



Just craniad of the midbrain is a small rather irregular area, 

 bounded craniad by the band-like optic chiasma (c), from 

 which arise the optic nerves (//), and showing caudad of this 

 band a rounded irregular projection (e). 'This is a fourth divi- 

 sion of the brain which is likewise covered dorsad by the 

 hemispheres; it is the 'tween-brain or diencephalon. Its 

 cavity is known as the third ventricle. Just craniad of the 



