312 ANATOMY AND PHYSIOLOGY 



over those parts has been demonstrated (Figs. 200, 202). Among 

 them are the centers for face muscles and for the upper extremity, in 

 the anterior central convolution; the centers for articulate speech 

 in the lower convolutions of the frontal lobe. Likewise the centers 

 for the special senses are fairly well known as for vision and 

 memory in the occipital lobe ; for taste in temporal; for touch in the 

 parietal; and for hearing and smell in the temporal and frontal. 



These centers are all connected directly or indirectly, by a 

 complicated system of association fibers (Fig. 201), so that by their 

 various impressions and nerve impulses they are constantly acting 

 with or upon each other. 



Illustration. The faculty of speech implies many previous 

 mental acts. The mind must know and recall the names of things 

 in order to mention them; it must have seen or heard things in 

 order to describe them and to have learned the words which ex- 

 press these conceptions. It may do all this and still be silent, 

 until these many factors are brought to work together under the 

 influence of the center for articulate speech which, as seen in the 

 diagram, is in close connection with those for the larynx, tongue 

 and face muscles. It is this center which determines when these 

 muscles shall be used for speaking instead of for other purposes. 



The first use of the faculty of speech probably represents the attempt to 

 reproduce a sound; next the impression of something seen, itself having a 

 sound of its own or a name. Gradually a feeling may come to find expres- 

 sion and so on through the endless line of impressions and memories, the 

 education of the speech-controlling center goes on; auditory, visual, sensory- 

 motor and other centers all contributing to this end. 



This is one illustration from many which might be cited, of 

 the value of association fibers. In general terms it may be stated 

 that the most highly organized brain has the greatest number of 

 association fibers, whereby the intellectual faculties of judgment, 

 reasoning and the will are developed. 



The centers which govern skeletal muscles belong to the convolutions 

 marked motor and cutaneous in Figs. 200 and 202. Tracing from below 

 upward the larynx, tongue, face, hand, arm and shoulder, foot, leg and 

 thigh are represented on the lateral surface, in the central convolutions border- 

 ing the Rolandic fissure; while other thigh centers and those for trunk, are 

 found on the medial surface bordering the longitudinal fissure. 



Note that a large portion of the cortex is devoted to complex 



