SUPPORT, MOTION, AND SENSATION 351 



plainly evident because of the transverse direction of its fiber, crossing 

 from one side of the cerebellum to the other. Nerve fibers arising in 

 the frontal, parietal, and occipital lobes of the cerebrum reach the 

 cerebellar hemispheres by way of the anterior -peduncles in front of the 

 pons, the latter bearing some resemblance to a pair of legs supporting 

 the body of the cerebellum. There is a second pair of lateral "legs" 

 behind the pons, the posterior peduncles, which contain communi- 

 cating fibers between the cerebellar lobes and the posterior regions 

 of the central nervous system. Thus, a highway of communication 

 with the cerebrum is at hand and herein lies a partial explanation of 

 man's ability to perform purposive acts as the result of the various 

 visual, auditory, and other impressions of the senses. Experimental 

 evidence indicates that this portion of the brain is primarily a seat of 

 muscular co-ordination. 



If the cerebellum of a dog is removed, the animal is unable to 

 co-ordinate its movements at first. Later it learns to walk, but the 

 gait is always slow and staggering. In a similar condition, a pigeon 

 is unable to fly, but like the dog, may eventually learn to walk again, 

 although resembling the proverljial inebriate in its gait. It has often 

 been claimed that man would make a better recovery after removal of 

 the cerebellum than either the dog or bird since his more highly 

 developed cerebrum would compensate the loss. In any case, from 

 these experiments the importance of the cerebellar region of the brain 

 in our everyday activities is better understood. 



The Medulla Oblongata or Myelencephalon. The brain at 

 this point is anatomically little more than an expanded region of the 

 si)inal column, but it is the sole means of communication between the 

 cerebrum and the body. Its dorsal surface is partially covered by 

 the posterior peduncles, and there is also a very thin non-nervous 

 roof, the mctatela, which covers the fourth ventricle, or the large cavity 

 of the brain of this region. Ventrally, two raised convex columns of 

 fibers may be seen, known as the pyramids. 



In the gray matter of the medulla, the controlling centers for many 

 of the essential functions of life are found, for example, the reflexes 

 concerned with the vasomotor and respiratory functions. Numerous 

 other centers that control swallowing, coughing, sucking, sneezing, 

 salivary secretions, gastric secretions, heart inhibition, and other 

 activities connected with the living body are located in the medulla. 



All of the cranial nerves, except the first four [)airs, arise from this 

 region. It is here, too, that the pyramidal tracts of transmitting fibers 



