INTERNAL FEATURES OF THE HUMAN BEAIN 



395 



supplies the muscles of the tongue. The first spinal nerve 

 of the frog corresponds to this nerve in action. 



Internal features of the human brain. — If we split the 

 brain in two by a vertical 

 cut, parallel to and a little 

 to the left of the longi- 

 tudinal fissure, we can 

 make out the following 

 parts on examining the 

 right side. (See Fig. 184.) 

 The fissure is seen to con- 

 tinue downward to a white 

 fibrous body which binds 

 the two hemispheres to- 

 gether. This is called the 

 corpus callosum. This band 

 curves in such a way as 

 to inclose a space actu- 

 ally outside the brain and 

 often called the "fifth" 

 ventricle. This fifth ven- 

 tricle is further inclosed by two thin membranes (the 

 septa lucida). The forward curve of this connecting body 

 below the fifth ventricle forms the roof of the midbrain, 

 and this part is called the fornix. Under the fornix is 

 the cavity of the midbrain or the third ventricle. This 

 third ventricle communicates with cavities in the right and 

 left hemispheres (the second or lateral ventricles) by two 

 openings in the fore part (the foramen Monroe). In the 

 figure, the opening into the right ventricle only appears. 

 The midbrain cavity is also extended forward in a funnel- 

 shaped tube called the infvMdibulum. 



Fig. 183 — Origin of cranial nerves; H, 

 heiuispheres; C. S. corpora striatum; P, 

 pineal body; Pt, pituitary body; C. Q. cor- 

 pora quadrigemina; Cb, cerebellum; Th, 

 optic thalamus; AT, medulla; /to XII, the 

 pairs of cranial nerves; Sp, i, 2, spinal 

 nerves. 



