218 CENTRAL NERVOUS SYSTEM 



the midline to reach the lateral lemniscus of the opposite side 

 with or without making connections with cells in the superior 

 olive. Other fibers join the lateral lemniscus on the same side. 

 In the lateral lemniscus the auditory fibers pass to the mid- 

 brain and end in the gray matter of the inferior colliculus, the 

 internal geniculate, and in the superior nucleus of the lemniscus. 

 From this termination another set of fibers, the auditory radia- 

 tion, continues forward through the inferior extremity of the 

 internal capsule to end in the superior temporal gyrus. Stimu- 

 lation of the cortex of the temporal lobe causes a pricking of 

 the ears and turning of the head and eyes to the opposite side. 



Smell and Taste Areas. The evidence for the situation of 

 these centres is scanty and dubious. In some cases of epilepsy 

 in which subjective sensations of smell were present the unci- 

 nate gyrus was found diseased. The olfactory tract may be 

 traced into this region. In animals of acute smell the uncinate 

 gyrus is large. The centre of taste is supposed to be situated 

 in the hippocampal convolution, posterior to the uncinate 

 gyrus. 



The Association Areas. The motor and sensory areas of the 

 cortex are surrounded by much larger areas known as associa- 

 tion areas, in which the different sense impressions are synthe- 

 sized into complex perceptions or concepts. These areas assume 

 their myelin sheaths at a later period and are not furnished 

 with projection fibers, as are the motor and sensory areas. They 

 are, however, abundantly connected with the latter by tracts 

 of association fibers. Knowledge is founded on sensations, 

 aroused through the various sense organs which are combined 

 in consciousness to form mental images. The sequence of phe- 

 nomena in the external world is orderly, and, corresponding to 

 this fact, the reflection of these phenomena in the sequence and 

 combinations of sensations is also orderly. In the association 

 areas memory records of past experiences are laid down in some 

 unknown material change in the combinations of nerve cells 

 and fibers. In these association or silent areas are included 

 considerable portions of the occipital, parietal, and temporal 

 lobes, nearly the whole of the island of Reil, and the greater 

 part of the frontal lobe. Here, and particularly in the latter 

 lobe, is the seat of intellectual processes. In the American 

 crow-bar case, a tamping rod, as the result of a premature 



