FIG. 9. A longitudinal section through a myelinated nerve fiber in the cortex of 

 a rat. The matrix of the axoplasm in this and similar instances is characterized by 

 the development of a large number of protein filaments <p/), which represent a 

 differentiation of the matrix (the keratin or myosin equivalent of this cell). These 

 are arranged with their long axes parallel to the long axis of the fiber. The ER is 

 represented by a very few membrane-limited profiles. The myelin sheath is shown 

 at ms, and mitochondria at m. The surrounding tissue comprises numerous non- 

 myelinated fibers and dendritic nerve endings. (Courtesy of Giuseppe Millonig.) 

 Magnification: 45,000 X. 



140 



