202 



AN AMERICAN TEXT-BOOK OE PHYSIOLOGY. 



Karvokinetic figures in mature nerve-cells utter injury have been demon- 

 strated, but we have yet to learn exactly what cells can exhibit this reaction, 

 and what becomes of them at the end of the nuclear changes. As there is no 

 reason to think that in mammals such a neoformation of neurones in the 

 nervous system lias any significance for the general physiology of the animal, 

 we shall pass the point with a mere reference to the literature. 1 



PART II.— THE PHYSIOLOGY OF GROUPS OF NERVE-CELLS. 



A. Architecture and Organization of the Central Nervous 



System. 



Since the nerves form the pathways by which the sensory surfaces of the 

 body are put into connection with the central system, and also the pathways 

 by which this system in turn is rendered capable of controlling the tissues of 



D.C 



V.R 



D.P 



Fig. 86.— Schema of the arrangement of the human spinal cord as seen in cross-section ; for clearness 

 the afferent fibres are shown on the left s i<U- only, efferent and central cells on the right side only (von 

 Lenhossek > : 1>. I'., dorsal ro"t ; V. /.'., ventral root ; 1>. P., direct pyramidal fibres; C. P., crossed pyramidal 

 films ; C., direct cerebellar tract; .1. L., antero-lateral tract ; D. C, dorsal columns. The various classes 

 nf cell bodies are Indicated by the manner of drawing. 



expression, it becomes at once important to determine over what nerves the 

 impulses arrive, how they travel through that system, and by what other 

 nerve- they arc again delivered :it the periphery. The arrangement of these 

 paths as found in the adult human nervous system is our principal object; at 

 the same time it should not he forgotten that the reactions of simpler mam- 

 malian systems have furnished the greater number of facts, and to them we 

 must constantly refer. 



General Arrangement of the Central Nervous System. — As the 

 typical arrangement of the neurones is found in the spinal cord, the schematic 

 representation (Figs. 86, 87) of a cross-section through this part will most 

 readily illustrate it. 



In accordance with this arrangement of the nervous system, as shown in 



1 Tedeschi, A , : .1 natomi&ch-ejcperimentellen Beilrag aim Sludien der Regeneration des Gewebe dcs 

 Centralnervensystems. Bcitriige zur palhologischen Anatomie und zur allegemeinen Pathologie, Jena, 

 1897, xxi. 43-72, 3 pi. 



