98 



EXPERIMENTAL PHYSIOLOGY 



needle point. Is it thicker or thinner than the dura mater? 

 Where are its blood vessels? What do they feed? What 

 are the functions of the three coverings of the brain? 

 C. The External Parts of the Brain. Examine the top of 



the brain. Note the two 

 convoluted hemispheres into 

 which the fore brain (cere- 

 brum) is divided by a fissure 

 (the longitudinal fissure). 

 Back of this appears the 

 wrinkled surface of the hind 

 brain (cerebellum). Is this 

 divided? 



Turn the brain over and 

 examine the lower surface. 

 Note the olfactory lobes on 

 the front part of the hemi- 

 spheres. What is their func- 

 tion? Back of these, locate 

 the optic nerves and note how they crc^s to form a chiasma, 

 so that the right eye is controlled by the left hemisphere, and 

 vice versa. Just back of this may be seen the pons, or bridge, 

 that connects the two sides of the cerebellum, and, coming 

 out in front of it on each side, the stalks (crura cerebri) which 

 spread out into the two hemispheres of the cerebrum. 

 Note that the stalks are the forward projections of a conical 

 spinal bulb, which comes between the cerebellum and the 

 pons, and is continued backward into the spinal cord. 

 This bulb is a part of the hind brain, and is called the me- 

 dulla. All along the under side of the brain are located the 

 cranial nerves, occurring in pairs. Beginning at the front 

 locate the pairs named in the following table : 



FIG. 47. Upper Surface of Brain (Hu- 

 man): 1, 2, two halves, or hemispheres, 

 of cerebrum; 3, 3, longitudinal fissure. 



