378 SPECIAL HISTOLOGY. 



proceed beyond them ? As true origins in the brain have never yet 

 been seen with certainty by any one, there remains nothing but physio- 

 logical analogies and reasons. As regards the former, we see in all the 

 spinal nerves, that they first penetrate transversely as far as the gray 

 substance, and then, only passing through this, join the white columns, 

 and we may thence suppose that the cerebral nerves, which, in general, 

 so closely resemble them, are in the same condition, and the more so, 

 because these also at first penetrate transversely into the interior of the 

 medulla, and the gray substance, with which they come in contact, 

 corresponds with that of the cord. To this may be added also, that if 

 we make the ten last cerebral nerves terminate in the gray substance, 

 into which they may so readily be traced, the decussated influence of 

 the parts above, upon them, which appears to be established by patho- 

 logical phenomena, cannot be explained in the case of any one of them 

 except the trochlearis, which decussates before it reaches its gray sub- 

 stance. Now, in the accessorius and hypoglossus it is actually possible 

 to see that the fibres come out from the gray substance, reached by 

 them in the first instance, and afterwards decussate ; and the same 

 thing is also at least probable* in the oculo-motorius ; so that I think it 

 may be, that all the nerves now in question undergo decussation, and 

 do not terminate in the so-termed nuclei of Stilling. Further investiga- 

 tion will have to show whether this [decussation] takes place in the 

 floor of the fourth ventricle, as would appear to be the case ; whether 

 all the fibres of these nerves take part in it ; and where the fibres pro- 

 ceed to after decussation. With respect to the latter, it may be sup- 

 posed from analogy with the spinal nerves, that the true origin of the 

 cerebral nerves is probably not in the medulla oblongata, but in the 

 corpora striata and optic thalami. Of that portion of the portio major 

 n. trigemini, which is continued into the restiform body, this may espe- 

 cially be remarked, that it certainly does not originate in that part, but 

 winds round it to somewhere above, as is the case also with the n. acces- 

 sorius. 



However, in stating, in accordance with what has been said, that I 

 do not consider it directly probable, that the sensitive and motor cere- 

 bral nerves originate in the medulla oblongata and pons, it is by no means 

 intended to imply that these parts may not, as central organs, exert 

 some influence upon them and the more deeply placed nerves. If the 

 medulla oblongata preside over the respiratory movements, if it and 

 the pons be the agents of multiplied reflex motions, this may be the 

 case, without its following that all the nerves called into action should 

 terminate in them, and simply for the reason that the gray substance, 

 so abundantly contained in them, influences the nerves which traverse 

 it, exactly as must be supposed to be the case in the spinal cord. 



