8 LISTER, ON INVOLUNTARY MUSCULAR FIBRE. 
Mr. Ellis, then, agrees with Mazonn in believing that the 
tapering fibre-cells of Kélliker owe their shape to tearing of 
the tissue; and he regards the nuclei as mere accidental ac- 
companiments of the proper muscular structure, probably 
belonging to the sheath of the fibres, which, according to 
him, are of rounded form and uniform width. 
The distinguished position of Mr. Ellis as an anatomist 
makes it very desirable that his opinion on this important 
subject should be either confirmed or refuted, and the object 
of the present paper is to communicate some facts which 
have recently come under my observation, and which, I hope, 
may prove to others as unequivocally as they have done to 
myself, the truth of Kolliker’s view of this question. 
In September last, being engaged in an inquiry into the 
process of inflammation in the web of the frog’s foot, I was 
desirous of ascertaining more precisely the structure of the 
minute vessels, with a view to settling a disputed point 
regarding their contractility. 
Having divided the integument along the dorsal aspect of 
two contiguous toes, I found that the imcluded flap could be 
readily raised, so as to separate the layers of skin of which 
the web consists, the principal vessels remaining attached to 
the plantar layer. Having raised with a needle as many of 
the vascular branches as possible, I found, on applying the 
microscope, that they included arteries of extreme minute- 
ness, some of them, indeed, of smaller calibre than average 
capillaries. A high magnifying power showed that these 
smallest arteries consisted of an external layer of longitu- 
dinally arranged cellular fibres in variable quantity, an 
internal exceedingly delicate membrane, and an intermediate 
circular coat, which generally constituted the chief mass of 
the vessel, but which proved to consist of neither more nor 
less than a single layer of muscular fibre-cells, each wrapped 
in a spiral manner round the internal membrane, and of 
sufficient length to encircle it from about one and a half to 
two and a half times. They are seen to have more or less 
pointed extremities, and are provided with an oval nucleus at 
their broadest part, discernible distinctly, though somewhat 
dimly, without the application of acetic acid. The tubular 
form of the vessels enables the observer, by proper adjust- 
ment of the focus, to see the fibre-cells in section; they are 
then observed to be substantial bodies, often as thick as they 
are broad, though the latter dimension generally exceeds 
the former. The section of the nucleus is in such cases 
invariably found surrounded by that of the substance of the 
fibre-cell, though occasionally placed eccentrically in it. 
From the circular form of its section the nucleus appears to 
