124 DEVELOPMENT OF NERVE-FIBRES. 



Several new facts have also been added concerning the development 

 of nerves, which tend to throw fresh light on the physiology of the 

 nervous system, since they render it almost certain that the central ter- 

 minations (or origin) of nerve-fibres are not disposed in loops, as until 

 lately has been generally supposed to be the case, but that they pass 

 directly into the nerve-corpuscles which compose so large a portion of 

 the grey substance of nervous centres. Both Muller and Remak, several 

 years ago, observed that from some of the corpuscles of the grey sub- 

 stance of the brain, spinal cord, and ganglia, fine tooth-like processes issue, 

 and may be sometimes traced to the extent of many times the diameter 

 of the corpuscles.* The resemblance which these processes bear to the 

 delicate, grey filaments observed by Remak in the sympathetic nerves, 

 led to the suggestion that the two are identical, and that the latter 

 filaments take their origin directly from the ganglion corpuscles. These 

 observations, however, do not appear to have attracted much further notice; 

 but it has been found by more recent investigations, that Remak's sugges- 

 tion concerning the origin of sympathetic nerve-fibres is perfectly correct, 

 and moreover that the fibres of the cerebro-spinal nerves also have, as was 

 indicated by Ehrenberg,| an exactly similar origin. J Without entering 

 into the details of these important investigations, the consideration of 

 which would be foreign to the present purpose, it may be remarked that in 

 the junction of the nerve-fibres with the ganglion-corpuscles, the contents 

 of the central part of the fibre (the axis-cylinder of Purkinje and Rosen- 

 thai, the primitive band of Remak) pass directly into the granular contents 

 of the corpuscle, while the fine external sheath of the nerve-fibre becomes 

 continuous with the membranous envelope, within which the granular 

 substance of the corpuscle is contained. The phenomena observed during 

 the development of nerve-fibres in the embryo, especially by Schaffner 

 and Kolliker, || agree very closely with these facts. In the earliest period 

 of its formation nerve-substance consists almost entirely of roundish, mostly 

 nucleated cells filled with a finely granular material, and, with the excep- 

 tion of being somewhat smaller, exactly similar to the nerve-corpuscles 

 found in the nervous centres of the adult animal. As the development 

 proceeds, but previous to the appearance of distinct nerve-fibres, many of 

 these cells send forth fine tubular processes of an apparently homogeneous 

 structure, which unite with similar processes from other cells, and thus, in 

 time, give rise to continuous nerve-tubules. Kolliker finds that in young 



* Muller's Physiology, vol. i. p. 657. f Structur des Seelenorgans. Berlin, 1836. 



ij: See Helmholtz, de Fabric. System. Nerv. evertebratorum. 1842 ; Kolliker, die Selbstand. 

 und Abhang. des sympath. nervensyst. Zurich, 1844 ; Dr. Will, in Muller's Archiv. 1844 ; 

 Dr. Todd and Mr. Bowman, Physiological Anatomy of Man, vol. i. p. 213; and more 

 especially R. Wagner, Neue untersuchungen uber den Bau und die endigung der Nerven und 

 die Struktur der Ganglien, Leipzig, 1847, and Dr. F. H. Bidder, zur Lehre von dem Nerven- 

 fasern. Leipsig, 1847. Schmidt's Jahrbiicher, 1847. 



|| An. des Sc. Nat. Zoologie, 1846, p. 104. 



