48 ON THE NERVOUS SYSTEM OF RANA PIPIENS. IV. 



principal fasciculi, one of which goes towards the head, and the other backwards ; 

 but some of the same fibres leave the principal bundles and run irregularly 

 amono- the cells. The sympathetic nerve fibres are more minute than the spinal, 

 and some of the latter may be readily traced into the sympathetic, where they are 

 distinguished by their size. A portion of the root c is, however, made up of the 

 more minute sympathetic fibres. The ganglion cells are well defined, lightly 

 pressed together, so that their spherical form is but slightly interfered with, and 

 contain a few granules of a yellowish color. In no instance was a caudate cell 

 noticed, nor any connection between the cells and the nerve tubes. The latter 

 passed among, but not into, the cells. Each ganglion formed by the union of the 

 spinal and sympathetic nerve may therefore be described as consisting of the fol- 

 lowing elements: 1st, a mass of ganglion cells; 2d, a fasciculus of sympathetic 

 fibres, some of which last become detached from the principal bundle, and, after 

 passing irregularly among the cells, either return to the fasciculus from which they 

 came, or join one of the other fasciculi ; 3d, a double series of filaments from a 

 spinal nerve, one series passing forwards and the other backwards ; some of the 

 fibres of each series become detached from their fasciculi, and pass irregularly 

 among the ganglion cells. 



Besides these ganglia connected with the spinal nerves, others more minute 

 appear to be formed wherever two sympathetic branches cross each other, in which 

 case the fibres of the diff"erent fasciculi separate and form an open but irregular 

 series of meshes, in which ganglion cells are deposited. In the formation of each 

 ganglion, it seems to be a general rule that there is an interchange of filaments 

 between the two or more trunks which enter into its formation ; also a deposit of 

 ganglion cells in the meshes formed by the separated fibres. In this last respect it 

 difi'ers from a plexus, which consists merely in the interchange of filaments of two 

 adjoining nerves, without any deposit of nerve or ganglion cells. 



From what has been stated with regard to the relation of nerve tubes and nerve 

 cells in the brain, in the spinal chord, and sj-mpathetic, it seems almost certain that 

 continuity of structure between the two histological elements of the nervous sys- 

 tem is in the species here desci'ibed not essential to nervous action. The only 

 conditions which direct observation gives evidence of is close proximity, but not 

 absolute continuity. 



