342 



NERyOUS 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 



li 



Fig. 138.— Ventral Surface ov the Brain. 

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

 N. oculomotorius; /F, N. trochlearis; F, N. trigeminus (I, mandibular nerve; 2, 

 maxillary nerve; 3, ophthalmic nerve; 4, sensory root); F/, N. abducens; 17/, N. 

 facialis; 17//, N. acuslicus; LY, N. glossopharyngeus; X, N. vagus; A'/, N. acces- 

 sorius; ' A7/, N. liyjioglossus. a, tractus olfactorius; fi, substantia perforata anterior; 

 r, optic chiasma; (/ infundibulum; f, hypophysis; /, lobus pyriformis, or tractus 

 postrhinalis; g, pedunculi cereliri; A, substantia perforata posterior; /, pons; y, sulcus 

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

 «, area elliptica; o, pyramidal tracts; /, anterior or ventral fissure; </, 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 showinj^ 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 



