OF THE NERVOUS SYSTEM IN GENERAL. 481 



only from the uniting of the cellulo-vascular system furnished 

 by the mother, with the nervous system furnished by the male 

 (Rolando)? Does the nervous system commence with the for- 

 mation of the cardiac ganglion, and develope itself succes- 

 sively by the great sympathetic nerve and the rest of the sys- 

 tem* (Ackermann)? 



What observation teaches us, is, that the nerves and the spi- 

 nal ganglions are formed before the spinal marrow, and this 

 latter before the encephalon, that is to say, before the cere- 

 bellum, the tubercles, and the brain. 



The spinal marrow, at first open behind like a groove, then 

 canaliculate, by the approaching of its borders, becomes finally 

 solid. It occupies at first the whole length of the vertebral 

 canal. The white substance which forms the exterior is first 

 deposited; the gray substance being deposited afterwards in 

 the interior, fills its cavity. 



The cerebellum, tubercles, and brain, which constitute at 

 first only the larger parts of the groove of the spinal marrow, 

 reverse themselves, meet, and unite at the median line, pre- 

 senting in the different places of their development, the most 

 exact resemblance with the same parts of fishes, reptiles, birds, 

 and mammalia, in ascending from the rodentia to the quad- 

 rumana [739]. 



In the brain as in the rest of the encephalon, and as in the 

 spinal marrow, the increase in thickness takes place simulta- 

 neously, exteriorly, and interiorly. It is by this circumstance 

 that we must explain, with Desmoulins, the existence of a 

 cavity which is found in the foetus, within the centrum ovale 

 of Vieussens, between the interior and exterior layers of the 

 vault of the lateral ventricles. 



In the encephalon as in the spinal marrow, the gray sub- 

 stance is only formed after the white, and even only after the 

 fibres of this latter are united by commissures upon the me- 

 dian line. 



After birth, the increase of the nervous system, previously so 



* Ackermann, de systematis ncrvei primordiis. Heidelb. 1813. Tiede- 

 mann, op. dt. 



