NERVES. 367 



specting the laws of development, it would appear to be a 

 perfectly justifiable and natural inference, that the nerve 

 tubes, when fully developed, have a similar mode of origin. 



According to some observers, certain nerve tubes are con- 

 nected with and take their origin from the prolongations with 

 which the caudate variety of ganglionary cells are provided : 

 this view, however, is confidently denied by many other in- 

 vestigators, and the point is one which is still involved in 

 considerable uncertainty : for myself I would observe, that I 

 have never succeeded in making a single observation favour- 

 able to such a conclusion. Notwithstanding, however, the 

 doubts which are now entertained respecting the modes of 

 origin of nerve tubes, the question is assuredly one which, at 

 some future day, will be satisfactorily determined by direct 

 observation. 



It is also still uncertain, whether nerve tubules originate in 

 the ganglia not included in the brain, as in those connected 

 with the encephalic nerves, and those of the sympathetic 

 system. 



When speaking in the preceding remarks of the origin 

 of nerves, that extremity of them is implied which is in con- 

 nexion with the brain and spinal cord: it is questionable, 

 however, in the case of the nerves of special sense, whether it 

 would not be more proper to consider their periphral rather 

 than their central extremities as their true origins ; a view 

 supported by the consideration that the sensations arise in, and 

 proceed from, the organs of the senses inwards towards the 

 brain, the great centre of nervous structure and force, as well 

 as by the fact, that the periphral extremities of these nerves 

 are generally, if not invariably, connected with ganglionic 

 cells ; such an association of the two elements is known to 

 exist in the eye, in the ear, in the nose, and probably exists 

 also in the papilla of the tongue and skin. 



Termination. It was not known until within the last four 

 or five years that nerves had any real termination : it was up 

 to that time generally considered that the nerve tubes in- 

 variably ended in the same manner as it is now supposed 

 that they originate, viz. in loops, and there can be little 



G G 3 



