351 



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 commissural 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 pharyngeal 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. 



By experiments that were made on the living worm, it is shown 

 that the pharyngeal chain of ganglia are independent of the other 

 nervous centres, although subject to their influence, and are not 

 only competent of themselves to preside over the complicated move- 

 ments of the suctorial pharynx and mouth, but appear also to be 

 centres of reflex action. 



The present memoir concludes with some observations and re- 

 marks on the ganglionic cords of other Invertebrata. 



