452 EMBRYOLOGY. 



favors the first view, His the last. All other investigators main- 

 tain that the fundaments of the ganglia, while they increase in size 

 and become spindle-shaped, are permanently united with the neural 

 tube by means of slender cords of cells which are metamorphosed 

 into the dorsal roots. If the latter view is correct, the dorsal roots 

 of the nerves must in time alter their place of attachment to the 

 neural tube by moving from the raphe laterally and ventrally. 



The discrepancy of these accounts is connected with the different 

 interpretations which exist concerning the development of the peri- 

 pheral nerves in general. 



(b) The Development of the Peripheral Nerves. 



When one reviews the various opinions which have been expressed 

 concerning the development of the peripheral nerves, it is found 

 that there are in the literature two chief opposing views. The 

 greater number of investigators assume that the peripheral nervous 

 system is developed out of the central, that the nerves grow forth 

 from the brain and spinal cord uninterruptedly until they reach the 

 periphery, where for the first time they effect a union with their specific 

 terminal organs. The outgrowth of the nerves from the spinal cord 

 was first asserted for the ventral roots and conjectured for the dorsal 

 ones by BIDDER UND KUPFFER. Their conclusions have since been 

 adopted by KOLLIKER, His, BALFOUR, MARSHALL, SAGEMEHL, and 

 others. However, views concerning the method of the formation of 

 the nerve-fibres are not in agreement. 



According to KUPFFER, His, KOLLIKER, SAGEMEHL, and others 

 the outgrowing nerve-fibres are processes of ganglionic cells located in 

 the central organ, which must grow out to an enormous length in 

 order to reach their terminal apparatus. There are at first no 

 cells or nuclei among them. These are furnished secondarily by 

 the surrounding connective tissue. According to the accounts of 

 KOLLIKER and His, cellular elements from the mesenchyme approach 

 the bundles of nerve-fibrillse, surround them, and then penetrate 

 into the interior of the nervous stem, at first sparingly, afterwards 

 more abundantly, and form around the axis-cylinders the sheaths of 

 SCHWANN. 



On the other hand, BALFOUR defends most positively the doctrine 

 that cells which migrate out of the spinal cord along with the nerves 

 share in the development. In his " Treatise on Comparative Embry- 

 ology " [vol. ii., p. 372] he remarks upon this subject : " The cellular- 



