230 



HUMAN PHYSIOLOGY 



CHAP. 



deep, and so increase the amount of 

 gray matter on the surface without any 

 material increase in the brain weight. 



1. Get a sheep's brain from your butcher and 

 find the cerebrum, cerebellum, pons, and bulb. 



2. Locate the frontal, parietal, temporal, and 

 occipital lobes of the cerebrum. 



3. Notice the fissures and convolutions in the 

 different lobes. 



4. Observe how the two hemispheres are 

 joined together. 



158. The Bulb. The bulb or medulla 

 is a slight enlargement at the upper end 

 of the spinal cord. It looks very much 

 like the cord, but it has a rougher sur- 

 face. The white matter of the cord 

 continues up through the bulb and leads 

 to cell bodies on the surface of the cere- 

 brum. In tJie bulb most of the nerve"' 

 fibers cross to tJic otJier side before they 

 go in or out. This explains how the left 

 side of the brain controls the right half 

 of the body, and the right brain the left half. When 

 the left brain is paralyzed, the organs on the right side 

 of the body are affected ; the right arm and the right 

 leg do not work as they should, for the nerves do not 

 stimulate them. 



There are nerve centers in the bulb that control many 

 of the higher reflex muscular activities, as breathing, 

 masticating, sucking and swallowing, sneezing, hic- 

 coughing, the secretion of digestive fluids and sweat, the 



FIG. 125. The ner- 

 vous system of a 

 pigeon. (Drawn 

 by Pratt.) 



