153 
cular fibres of the ventricle of the smallest and thinnest 
heart. They change the planes in which they ramify so 
continually that, in preparing sections thin enough for obser- 
vation, we should inevitably fail to trace the same fibre, even 
for the distance of tlie jjotli of an inch. In the thinnest 
part of the auricle, however, we have an extended section 
already made for us; and in the hyla this is so very thin 
that there is but a single layer of muscular fibres, and I have 
succeeded in tracing the nerves amongst the delicate ramifi- 
cations of the reticulated muscular tissue for a considerable 
distance. See PI. XIII, fig. 1. 
Distribution of the nerves to the muscular fibres . — In this 
beautiful texture the finest branches of nerves are seen to 
form networks amongst the muscular fibres. No end-organs 
or end-plates of any kind are to be detected anywhere ; but 
so fine are the fibres, and so separated from one another, that 
if such organs existed they could hardly escape observation, 
more especially as we find, very clearly demonstrated, 
nerve-fibres very much finer than those connected with 
the so-called end-organs in other situations ; nor does the 
nerve- fibre penetrate the sarcolemma, for in these muscular 
fibres this structure is absent. Bundles of fine, pale, “ nucle- 
ated ” nerve-fibres are seen ramifying amongst the muscular 
fibres, and dividing into finer and still finer branches, the 
finest being less than T o o'ou o ^ 1 °f an inch in diameter, but . 
these can, nevertheless, be followed for long distances. The 
masses of germinal matter of the nerves (nuclei) are often 
situated very close to the muscular fibres, as in the lower part 
of fig. 2, to the right ; but they can, nevertheless, be seen to 
be connected with the nerve-fibres only, and not with the 
muscular tissue. 
The nerve-cells . — The only nerve-cells in the cardiac ganglia 
are the oval or pyriform cells I have fully described else- 
where. Some have but two fibres, but many have five or six, 
or even more, which may run parallel to or be curled spirally 
round one another for a short distance from the cell ; but 
they do not run far before they pursue opposite directions as 
they pass from the cell with which they are connected. I 
have preparations of the thin part of the auricle of the frog’s 
heart, in which fibres can be seen to leave the ganglion-cells 
and be followed for some distance to their ultimate distribu- 
tion upon the muscular fibres. 
Fig. 1. — I have figured a single ganglion-cell with 
its straight and spiral fibres. I have not, indeed, succeeded 
in tracing a nerve-fibre from the cell to its peripheral distri- 
bution and back again to the same cell ; but at the same 
