1862.] 81 



onic cells, single or in small clusters, on the larger branches distri- 

 buted to the venous sinus and the auricles, but none on those of the 

 ventricle ; so that the ganglionic matter of the ventricle exists only 

 at its venous aperture. 



Respecting the microscopic structure of these parts, it is known 

 that amongst the ganglionic cells there are many which give origin 

 each to only one nervous fibre, and have therefore been termed uni- 

 polar cells, whilst there are others that apparently give off no fibres, 

 and are named apolar cells ; but it is as yet altogether unknown 

 whether the proper or radical fibres of the vagi connect themselves 

 with the ganglionic cells of the heart or not, and it is equally uncertain 

 from what immediate source the nerve-fibres proceeding to the mus- 

 cular substance of the heart are derived. 



Most physiologists seem to believe that the fibres of the vagus or 

 pneumogastric are not directly distributed to the muscular fibres of 

 the heart, but that they act only through the medium of the gan- 

 glionic cells, and that the fibres derived from these cells are the real 

 motory nervous elements. So far as I know, however, notwith- 

 standing its importance, no one has hitherto examined into this matter. 



My own inquiry has had a twofold object : first, to ascertain the 

 relation of the pneumogastric to the ganglionic cells ; and secondly, 

 to find out the mode of termination of the ultimate divisions of the 

 nerves on the muscular fibres. 



As regards the first question, all my observations tend to show that 

 the nervous system of the frog's heart is constituted on a very simple 

 principle. There are, in fact, two distinct although associated systems 

 of nervous fibres distributed to every part of the muscular walls of 

 the heart : namely, first, the proper or radical fibres of the vagus, 

 which pass through the ganglia of the heart, without, so far as I can 

 discover, connecting themselves with the ganglionic cells, and proceed 

 straightway to the muscular fibres ; and secondly, fibres derived from 

 ganglionic cells, which are associated with the original vagus-fibres, 

 and run with them to the muscular tissue. 



The obvious bearing of this matter on important questions of phy- 

 siology requires that I should here explain the grounds on which the 

 conclusion now stated is founded. On this head I have first to state 

 that, in following with the microscope and with the aid of potash the 

 fibres of the vagus as they pass through the several ganglions of the 



VOL. XII. G 



