INTOLIJNTAIIT MTJSCULAE TISSUE OE THE UEINAET BLADDEE. 
475 
and diminishing in size, with oftentimes wavy ends, gradually to cease amongst the sur- 
rounding tihrous tissue, as in fig. 7 of the same Plate. 
Structure of the Muscular Fibres. 
The characters of the fibres of the bladder above detailed do not lend support to the 
doctrine of the cell-structure, as explained by Professor Kollikee, but rather lead to the 
supposition that in construction, as in other respects, the two kinds of muscular tissue 
have something in common ; and after careful examination I am induced to believe 
that the ultimate composition of the two is not dissimilar. To me the fibres seem to be 
made up of very minute threads — the ultimate fibrils — as in the voluntary muscle. Indi- 
cations of this composition are manifested by longitudinal marking, both with and with- 
out the action of dilute nitric acid ■*, and by the separation of the component parts when 
a fibre is about to end in its tendon, as before described. It is not possible to detach at 
pleasure one of the ultimate fibrils making up a fibre, as in the voluntary muscular 
tissue, and possibly from some difference in their uniting medium ; but partial acci- 
dental separation of them in small bundles, about ^ 4 Vooo ^^ of an inch wide, is not very 
unfrequent. 
I have not succeeded in distinguishing any sheath or sarcolemma to the fibres of the 
bladder ; but by the action of dilute nitric acid the fibres present oftentimes a rough and 
uneven appearance, as if some encasing material was partly removed. 
There seems to be also a further resemblance in structure between the involuntary 
and the voluntary muscle. 
In the voluntary muscular fibre the ultimate fibril is composed, as is well known, 
of small elongated dark pieces — the sarcous elements, which are united by a transparent 
material, and give rise by their arrangement to the transverse markings or strise of the 
fibre. 
On viewing a clean and separate fibre of the bladder with a magnifying power of 600 
diameters, it may sometimes appear fibrillated, as in Plate XXVII. fig. 4 «, but at 
other times a fibre will have a granular or dotted surface ; just as there may be a differ- 
ence in the surface-marking of the voluntary fibre, the longitudinal striation being most 
conspicuous in one specimen and the transverse marking in another specimen. In the 
large and somewhat flattened fibres, the dark spots, though of small size, are lengthened 
rather than rounded, and have a linear arrangement in a clear matrix (see fig. 6), though 
only a small portion of the line of dots will be in focus at the same time, in con- 
sequence of the high magnifying power employed. These dots seem to me to indicate 
the existence of small opake masses — sarcous elements of the involuntary muscular 
tissue of the bladder, which are the representatives of the sarcous elements of the 
* Dilute nitric acid, 20 per cent, strong, has been recommended as suitable for showing the cell-structure 
of the involuntary muscular substance ; but if the microscopist desires to see fibres as they are here described, 
he must refrain from using that mixture. By the action of the acid the fibres are softened so that they will 
tear readily in any direction, and are deprived of the tendons attaching their ends. 
