Meyer, Data of Modem Neiitology. 147 



the differentiation, or dissociation, becomes more prominent ; 

 the association is naturally also implied by the anatomical ar- 

 rangement.) 



The practical and didactic value of the above plan of the 

 nervous system is quite evident when we take as an instance a 

 section of the nervous system. The first question after a gen- 

 eral orientation as to the presence of a central canal and the 

 distribution of gray and white matter is this : Are there any 

 segmental elements — motor neurones and afferent neurones ? 

 Which segment do they belong to ? Cord, medulla, midbrain, 

 or which part of the neural tube ? Are there any cells and 

 fibers of the ground bundle (intersegmental) formation ? Cere- 

 bellar dependent parts? Midbrain dependent parts? Cerebral 

 dependent parts ? Any non-classified elements ? 



[To be Continued.] 



DESCRIPTION OF FIGURES. 



Plate XV. 



Fig. I. A, Interrelation of afferent and efferent cells, according to Nansen 

 (and Golgi). 



B. Interrelation of afTerent and efferent neurones in the cortex, according 

 to the idea of van Gehuchten and Cajal. From Ramon y Cajal, Nuevo con- 

 cepto, etc., 1893. 



Plate XVI. 



Fig. 2. Diagram of the nervous system of Lumbricus. From Schaefer, 

 Brain, XVI, p. 154. 



Plate XVII. 



Fig. J. Human embryo of 10 mm. length (see the cross-section of rhomben- 

 cephalon). Development of the " segmental nervous system " perfectly plain. 

 Supra-segmental mechanisms barely indicated as Anlage of the cerebrum and 

 cerebellum. Afferent neurones blue, efferent neurones red. His, Geschichte des 

 Gehirns, Plate II. 



Plate XVIII. 



Fig. 4. Cross-section of the rhombencephalon of a human embryo 10 mm. 

 long, X 40. Motor pneumogastric and hypoglossal nuclei with " ascending " 



