ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 



463 



that when the cell bodies to which nerves are attached are 

 destroyed in any way, these nerves at once die to their per- 

 iphery. By this method it was possible to destroy certain 

 brain centers and thus destroy the entire bundle of nerves 

 leading out from it. This, o"f course, enabled the observer 

 to determine over what part of the body the nerve centers 

 in question had jurisdiction. It was this method of degen- 

 eration that helped materially in giving us our knowledge 

 as we now have it of the courses of the fibers in the spinal 

 cord. 



THE PHYSIOLOGICAL TOPOGRAPHY OF THE BRAIN. 



1. The Motor Areas. The motor areas of the brain lie 

 along the fissure of Rolando. At the top of this fissure are 

 the motor areas governing the toes. These are followed by 

 motor nerves which govern regions gradually higher up, 

 until at the bottom of the fissure of Rolando we come to 

 those motor areas concerned in the control of lips, larynx 

 and mouth. The proximity of these motor centers to the 

 speech center on the left side is worth noting. 



2. The Seat of Conscious Tactile Sensations. But not 

 only are these motor centers concerned in the production of 

 the voluntary impulses. They are also the seat of the sen- 

 sations which arise in the portions, the motions of which 

 they control. Thus the motor area along the fissure of Ro- 

 lando governing the muscles of the finger is probably also 

 the center in which the sensory impulses coming from the 

 finger are finally interpreted as conscious sensations. This 

 area ought, therefore, more properly to be called the motor- 

 sensory area. 



3. The Visual Center. In the occipital lobes the visual 

 center is located. It is of interest to point out here that 

 while for the motor areas the right side of the brain gov- 

 erns the left side of the body, and vice versa, there is not 

 such a complete crossing for the optic nerves. There is, in 

 fact, in the optic nerve only a half crossing. In the right 



