386 



Dr. W. H. Gaskell. ' Structure, Function, [Feb. 23, 



The so-called motor root of the Vth nerve is therefore a complete 

 nerve belonging to the same group as the Illrd, IVth, and Vlth, and 

 does not require the sensory portion of the Vth to make it resemble 

 a spinal nerve. 



Leaving aside for the moment the consideration of the sensory part 

 of the Vth nerve we come to the Vllth nerve ; here we find the 

 anterior root manifestly composed of a large-fibred and a small- 

 fibred portion, the latter being derived mainly from the n. inter- 

 medins, though some of the fibres are in the roots of the facial itself. 

 The ganglion geniculatum bears the same relation to these small 

 fibres as the ganglion oculo-motorii to those of the Illrd nerve, and 

 ganglia which are still f urther vagrant are seen in the submaxillary 

 ganglion, &c. The ganglion of its posterior root is found in the root- 

 lets of the facial in the usual position, directly after their exit from 

 the brain, and in man both nerve fibres and nerve cells are degene- 

 rated in the same way as in the case of the cranial nerves already 

 considered. 



The cranial nerves considered up to this point form a natural 

 group all arranged on the same plan with a ganglionated and non- 

 ganglionated anterior root, and a phylogeneticaJly degenerated 

 posterior root and ganglion. 



Passing now to the nerves of the medulla oblongata, we find 

 another group with different characteristics. Here there is no sign 

 of any degenerated posterior roots or spinal ganglion ; here we find 

 not degeneration of any component but separation of the component 

 parts of a spinal nerve, so that the separate nerves no longer, as in 

 the previous cases, represent each a perfect nerve. Thus in the IXth, 

 Xth, Xlth, and XHth nerves of man at all events, the somatic por- 

 tions of the posterior roots are absent in the nerves themselves with 

 the exception of the auricular branch of the vagus, but clearly are 

 not absent in reality, for the structure of the medulla oblongata shows 

 that they have become diverted from these nerves to help form the 

 sensory part of the Vth, and the Gasserian ganglion. The somatic 

 motor part of this group is present, not as forming a part of each 

 nerve, but as a separate nerve, the hypoglossal or XITth nerve, the 

 nucleus of origin of which extends along the whole length of the 

 medulla oblongata. The ganglia jugularia of the IXth and Xth 

 nerves which give origin in the Sauropsida to the laryngopharyngeal 

 nerve, are the spinal ganglia of the splanchnic portions of the 

 posterior roots of this group, while the ganglion petrosum of IX, and 

 the ganglion trunci vagi (the vagrant character of which is well 

 shown in such animals as the crocodile) are the motor ganglia of the 

 small-fibred portions of the anterior roots of these nerves. Finally, 

 the non-ganglionated splanchnic large-fibred motor nerves have not 

 separated off to form a separate nerve like the XHth, but remain as 



