1888.] and Distribution of the Cranial Nerves. 



387 



the motor nerves of the laryngeal and pharyngeal muscles. In fact, 

 the IXth and Xth nerves with the medullary part of XI contain all 

 the splanchnic elements belonging to a spinal nerve, or rather a group 

 of spinal nerves, and in man at all events contain none of the somatic 

 elements (with the exception of the auricular branch of the vagus), 

 the somatic portions being represented by the hypoglossal, and a 

 portion of the sensory root of the trigeminal. 



Turning our attention to the sensory root of V, we see no sign of 

 any degenerated ganglion or degenerated posterior root ; it clearly 

 possesses a functional, well-developed spinal ganglion, the Gasserian ; 

 and according to human anatomists, it is exclusively derived from 

 the ascending root of the Yth nerve, i.e., it arises in close connexion 

 with the posterior horn along the whole length of the central nervous 

 system comprised between its point of exit and the middle of the 

 cervical region of the cord. In the absence, then, of any signs of 

 degeneration among its fibres, combined with the presence of a dege- 

 nerated posterior root ganglion in the so-called motor root of V, we 

 may, I think, fairly conclude from the peculiarity of its origin that the 

 sensory part of V and the Gasserian ganglion does not represent the 

 posterior root of a nerve of which the so-called motor part of V is 

 the anterior root. The explanation of the peculiarities of the origin 

 of the sensory somatic elements of the ascending root of V, as well as 

 of the corresponding sensory splanchnic elements of the ascending 

 root of X must be sought for in the explanation of the presence of 

 the degenerated posterior root ganglia of the Group I of cranial 

 nerves already mentioned. 



As far as VIII is concerned, it will suffice at present to say that it 

 does not possess an undoubted degenerated ganglion, that part of it, 

 at all events, possesses a functional spinal ganglion, and that it is a 

 complex nerve, the structure of whieh requires a much more extensive 

 investigation than I have as yet been able to give it. 



In connexion with the presence of these degenerated posterior 

 roots and spinal ganglia, it is significant that in the region of the 

 brain from which these roots spring, groups of strongly pigmented 

 cells are found, the reason for the presence of which is unknown. 

 Of these groups the cells of the locus cceruleus are in structure and 

 position clearly the termination of Clarke's column, and are therefore 

 in all probability connected with the remnants of the small-fibred 

 ganglionated efferent portions of some of the nerves of this group ; 

 the cells, on the other hand, of the Substantia nigra are in apparent 

 connexion with and are embedded in the direct continuation of the 

 degenerated posterior root fibres of the Illrd nerve. 



To sum up, then, it is clear that apart from I, II, and VIII, the 

 rest of the cranial nerves are built up on the same type as the spinal 

 nerves, and that their peculiarities are such as to divide them into 



VOL. xliii. 2 F 



