256 Royal Society : — 



nect together the two lateral halves of the entire chain in and through 

 the cephalic ganglion, which is their dominant and controlling 

 centre. 



Two parts of the human brain may be compared to this transverse 

 cephalic band. One is the arched and commissural band of fil)res 

 prolonged through the corpora quadrigemina, from the upper and 

 inner part of the fillet on each side. But the outer part of the fillet 

 turns forwards and upwards beneath the corpus geniculatum internum 

 and optic tract, to enter the optic thalamus. It is not improbable, 

 therefore, that some of the fibres of the tract may descend along 

 this portion of the fillet, to form loops with the roots of the fifth 

 nerve, over which it passes, since in Lnmbricns it has been seen that 

 many of the roots of the cephalic nerves run down the pharyngeal 

 crus to form loops with others to which it gives origin. In a former 

 memoir by the author, it was shown that some of the roots of the 

 spinal accessory nerve reach the anterior grey cornu and mingle, 

 perhaps pass out with, the spinal roots ; and he has since observed 

 the equally interestirig fact, that the same nerve forms a similar 

 connexion with the vesicular nucleus of the hypoglossal, which may 

 be considered a representative of the anterior spinal. The spinal- 

 accessory, therefore, takes its origin from at least three different 

 sources, — from its own nucleus, and from the nuclei of the hypo- 

 glossal and anterior spinal nerves. The peripheral communications 

 of both the former with the latter nerves in the cervical plexus is 

 well known. The author believes he has also made out an intimate 

 connexion by loops between at least the portio intermedia of the 

 seventh and the large root of the fifth nerves within the substance of 

 the human medulla. 



The other part of the human brain which is analogous, or homo- 

 logous with the cephalic band of Lumbricus, is the corpus callosum. 

 Gall and others have thought that the fibres of this structure arise 

 from the grey substance of the hemispheres ; while some have 

 endeavoured to show their continuity with those of the crura cerebri. 

 Now it is quite certain that in the cephalic ganglion of Lumbricus, a 

 large proportion of the conmiissural fibres are directly continuous 

 with those of the pharyngeal crura ; and there are appearances which 

 favour the conclusion that some of the latter are confined to the 

 lobe on their own side. From analogy, then, we may infer, that 

 while a large portion of the crura cerebri are directly continuous with 

 the corpus callosum, some of their fibres probably terminate in the 

 cerebral convolutions of the corresponding side. 



From what has been shown, it is evident that the communications 

 between the roots of nerves are more intimate and extensive than 

 they were hitherto believed to be ; for it has been seen that the roots 

 not only of every spinal nerve, but of every other in the system, 

 communicate with those which correspond on the opposite, and with 

 those which are adjacent on the same side. Of the cephalic with the 

 two sets from the phar^aigeal collar, and of the latter with each 

 other, the connexions are particularly interesting, and may serve 

 as guides to future investigations on other forms of the nervous system. 



