324 ANATOMY AND PHYSIOLOGY 



Concerning the reception and originating of ideas, the exercise 

 of thinking in other words, intellectual processes we know 

 only that these activities certainly depend for their normal 

 manifestation upon a normal cerebrum. A well-developed cere- 

 brum has good convolutions and deep furrows, and white fibers 

 in good connection with its several parts. These indicate mental 

 power, being of more importance than the mere size of the brain. 

 The brain of the infant possesses all of the interior parts, as 

 ganglia, etc., but the cortex is almost smooth. The cortical cells 

 are immature and many axons have not become sheathed. With 

 the growth of the child and quickening of the mind, the convolu- 

 tions and furrows appear and develop; the cortical cells mature 

 and the white fibers become sheathed. (The brain fiber does not 

 conduct impulses before its sheath is complete.) 



The number of association fibers (Fig. 201) is an index of the 

 mental power of a brain. Large association areas signify a large 

 expanse of cortex with power to register, remember and compare 

 a multitude of sensations from various sources and the ability 

 to reason about them and form opinions concerning them. 



The sympathetic division of the nerve system is the medium 

 of communication (through communicating branches) of nerve 

 impulses between the cerebro-spinal system and the organs con- 

 cerned in involuntary processes, notably those connected with 

 nutrition and growth, through control of secreting cells and vessel 

 tone. 



showing the relation of the gray to the white matter; p.c. a volitional or motor cell; 

 d.a. a descending axon or nerve-fiber connecting the volitional cell from which it 

 arises with the motor cell in the spinal cord; s.c. a sensor cell; a.a. an ascending axon 

 or nerve-fiber connecting a receptive cell from which it arises (not shown in the dia- 

 gram) with the sensor cell in the gray matter of the cerebrum. -The nerve-fibers 

 which pass outward from the spinal cord to the glands, blood-vessels, and the 

 muscle walls of the viscera, have for the sake of simplicity been omitted from the 

 diagram. 



