ABSTRACT
Identifying the paths that nerve fibers take as they extend from the brain and spinal cord to target areas throughout the body has been of interest to scientists for centuries (Figure 1.1), but significant advances in understanding how such pathways form during development did not occur until the mid-to late nineteenth century. During this period, detailed descriptions of the microscopic anatomy of neural tissue were described for the first time. These new findings were made possible by several technical advances arising during that period. One such technological development was the introduction of the microtome, an instrument that provides a means to cut tissues into very thin slices. Another was the increasing availability of microscopes with improved optics that allowed for better visualization of these thinner tissue slices. Additionally, scientists continued to test and refine techniques for fixing (preserving) and staining tissues, so that by the end of the nineteenth century, several improved methods for visualizing the cellular composition of tissues were available. These innovations led to discoveries that were part of the “great age of cellular biology,” laying the foundation for many fundamental concepts that we now take for granted.
