324 NERVOUS SYSTEM. 



Bell to bring forward a system of no small importance, on the 

 anatomy and physiology of the nervous system.* 



The development of the nervous system is amongst the ear- 

 liest processes in the distinct evolution of the foetal organs.f 

 At the end of the first month, when the head is a mere swell- 

 ing of one end of the small maggot-like being, the brain and 

 the spinal marrow are not by any means distinct, but the parts 

 being transparent, a limpid fluid holds their place. About the 

 fifth or sixth week, the embryo having acquired a length of five 

 or six lines, the rudiments of the brain appear as vesicles con- 

 taining a whitish and almost diaphanous fluid, while the spinal 

 marrow represents a long canal containing the same, and com- 

 municating with the cerebral vesicles. 



In the early part of the third month, the brain and spinal 

 marrow show very distinctly the rudiments of the several ca- 

 vities, elevations, and fasciculi, which mark their subsequent 

 mechanical arrangement of surface ; and from this period it is 

 no longer difficult to trace the successive development of 

 each part to the degree of perfection which it has at the time of 

 birth. 



From the many observations made by Tiedemann on these 

 points, he has deduced the conclusion, that the brain is produced 

 by the superior part of the spinal marrow ; that is to say, by the 

 medulla oblongata, which grows and is developed for the pur- 

 pose. That this is proved, in the extension upwards and for- 

 wards of the two principal fasciculi of the spinal marrow, and 

 by a canal which is found in the spinal marrow of the foetus, 

 being extended to the fourth, and even to the third ventricle; 

 also, by the cerebellum proceeding evidently from the medulla 

 spinalis, since its two crura may be traced growing from it, and 

 subsequently uniting over the fourth ventricle, so as to form the 

 especial structure of the cerebellum; also, by the tubercula 

 quadrigemina being derived from the corpora olivaria of the 



* The same subject has been taken up, in an inaugural thesis, by a zealous 

 and intelligent graduate of the University ; and, by a series of ingenious experi- 

 ments, seems to have been generally proved and illustrated. Chapman's Med. 

 andPhys. Journal, 1823, vol. vi. p. 240. Remarks on some of the Nervous Func- 

 tions, by J. P. Hopkinson, M. D. 



f Anat. du Cerveau, par F. Tiedemann, traduit par Jourdan, Paris, 1823. 

 Anat. Comp. du Cerveau, par E. R. A. Serres, Paris, 1824. 



