82 [May 1, 



heart, it is easy to see that they run through these hodies without 

 forming any connexion with the ganglionic cells. Of course I do not 

 pretend to have traced every individual fibre, hut I can speak positively 

 of the large majority, and conclude that the same holds good generally, 

 the more so as the ganglion-cells themselves present conditions which 

 corroborate this conclusion. These cells, that is to say, all of them 

 which are connected with nerve-fibres and whose connexions can be 

 clearly made out, are unipolar, or send out but a single fibre, and 

 that in a peripheral direction, without having any connexion with the 

 transcurrent fibres of the vagus. Bipolar or multipolar cells are not 

 to be seen: some apparently apolar cells present themselves, but 

 concerning these it may be doubted whether they are not unipolar 

 cells whose issuing fibre is in some way hidden from view. I may 

 add that, as the cells lie mostly at the side of the vagus and its branches, 

 and not amongst its fibres, their relation to the latter is less difficult 

 to determine. 



From what has been said I feel justified in my conclusion that 

 there are in the frog's heart two distinct systems of nervous fibres, 

 one ganglionic, the other directly proceeding from the vagi or pneu- 

 mogastric nerves. 



Before proceeding, in the next place, to describe the terminations 

 of the nerves, I have to explain that the muscular tissue of the frog's 

 heart is entirely made up of short spindle-shaped uninucleated fibres, 

 or fibre-cells, resembling in every respect those described by me in 

 the involuntary muscles generally, except that they have very distinct 

 transverse striae. These striated fibre-cells, as correctly described by 

 Weismann, are arranged so as to form larger and smaller bundles, 

 and these unite into a network which, in each of the three parts of 

 the heart, is continuous throughout. Now, respecting the nerves, it 

 is easy to show that their smaller branches, composed of dark-bordered 

 fibres from the vagus and the ganglion-cells, also form a general net- 

 work, with larger and smaller meshes, on or between the secondary 

 muscular fasciculi. As the ramifications become finer the component 

 nerve-fibres gradually lose their medullary sheath, and are finally 

 continued into pale nucleated filaments which lie singly or two or 

 three together in the finest musculat bundles. The last terminations 

 are pale, nucleated fibres, entirely agreeing in aspect with those de- 

 scribed as the ends of the sentient nerves in the voluntary muscles. 



