THE FIBRE-TRACTS.
The older anatomists contented themselves with the task of describing the brain simply from the exterior and, in a sense, without further leading conceptions. In this period originated the terminology that owes its existence to merely purely superficial and accidental resemblances. As examples, one recalls the designation of the corpora quadri gemina as the " nates" and " testes," the suggested resemblance of the corpora mamil laria to the female breasts, of the calcar avis to the cock's comb, of the Lyra Davidis to a harp, or of the fornix to an arch.
In order to render more exact investigation possible, the pioneer observers first sought to overcome the softness of the central nervous substance, and to that end employed various chemical agents, as alcohol, corrosive sublimate and salt solutions. Cold was also used to give the brain greater consistence, and, indeed, Gennari and Reil made their observations on frozen brains. In this manner, in a purely morphological way, began the foundation of the study of the internal connection of the individual brain-segments and. until the middle of the nineteenth century, the method of direct mechanical dissociation of the alcohol-hardened brain was employed to demonstrate the chief fibre-tracts (Gall and Spurzheim, Burdach, Reil, Arnold, Foville).
A distinct advance in brain-anatomy was made when the structure of the central nervous system began to be studied from the standpoint of development. In this Tiedemann and Reichert were pioneers. In the introduction to his " Anatomie and Bildungsgeschichte des Gehirns," Tiedemann observes that the origin and development of the brain were an almost totally neglected part of anatomy and physiology. He mentioned the law formu lated by Harvey, that the embryo of man and of the animals does not appear in a com pleted and only diminished form, but that it begins with a simpler form, successively passes through lower formative stages and finally reaches a higher stage of development. Why, says Tiedemann, should not a similar progression from a simpler to a more complex structure also occur in the construction of the brain of the embryo and of the foetus ; and, further, should not this process supply explanations concerning the form and struc ture of the brain, so intricate in its completed condition? Tiedemann busied himself for several years with the construction of the embryonal and foetal brain. The pure mor
phology of the brain, however, reached high-water mark with the embryological method of examination followed by C. B. Reichert. Through the work of Schmidt, Mihalkovics, Kolliker, His and others, this method has led to a strict scientific division of the brain and to the establishing of a comprehensive morphological basis.
By these "embryological" methods much was gained, but by no means all. Embryology taught us to understand the development of the form, but told us nothing concerning the intimate connection of the parts, a clear insight into which alone leads to a comprehension of the function of the central nervous system. The question of the intimate connection of the parts, however, is nothing but the question of the fibre-tracts and there with we enter a new phase of brain-investigation. We may designate this phase as the physiological in contrast to the pure morphological, since the extraordinarily difficult and laborious endeavors of the later investigators to unravel the intricate fibre-complex of the central nervous system are all undertaken from the physiological standpoint and with a physiological aim.
After Helmholtz had shown for the invertebrates and Remak for the vertebrates, that the nerve-fibres proceed from the nerve-cells, it became evident that the simple method of dissociation no longer sufficed. What neurology had then to attempt was not merely the accurate description of the external form, but, before all else, the estab lishing and the tracing of the intricate paths which the nerve-fibres pursue, and the definite establishment of all the numerous connections joining centre with centre within the interior of the central nervous system and bringing the latter into relation with the periphery. Although tracing these fibre-paths even within the peripheral nerves is by no means easy because of the peculiar plexus-formation and anastomoses of certain nerves, such task is especially difficult within the brain and spinal cord, since here often within a small space the most diverse paths run side by side and, further, decussations and interfeltings of the nerve-fibres make the direct tracing of the nerve-tracts impossible.