724 



NEUROLOGY 



some cell types is termed the cone of origin. These granules disappear (chromato- 

 lysis) during fatigue or after prolonged stimulation of the nerve fibers connected 

 with the cells. They are supposed to represent a store of nervous energy, and 

 in various mental diseases are deficient or absent. The nucleus is, as a rule, a 

 large^ well-defined, spherical body, often presenting an intranuclear network, and 

 containing a well-marked nucleolus. 





FIG. 627. Pyramidal cell from the cerebral cortex 

 of a mouse. (After Ramon y Cajal.) 



FIG. 628. Cell of Purkinje from the cerebellum. Golgi 

 method. (Cajal.) . Axon. b. Collateral, c and d. 

 Dendrons. 



In addition to the protoplasmic network described above, each nerve cell may 

 be shown to have delicate neurofibrils running through its substance (Fig. 629); 

 these fibrils are continuous with the fibrils of the axon, and are believed to 

 convey nerve impulses. Golgi has also described an extracellular network, which 

 is probably a supporting structure. 



Nerve Fibers. Nerve fibers are found universally in the peripheral nerves 

 and in the white substance of the brain and medulla spinalis. They are of two 

 kinds viz., medullated or white fibers, and non-medullated or gray fibers. 



The medullated fibers form the white part of the brain and medulla spinalis, and 

 also the greater part of every cranial and spinal nerve, and give to these structures 



