MOVEMENTS OF VOLUNTARY MUSCLE. 
467 
but as many persons are apt to be sceptical as to the credibility of the results of 
researches of this nature, with whatever uniformity obtained, it is necessary as well 
as interesting to corroborate every observation by others, in which the same structure 
is brought into view under a variety of aspects. In a subsequent part of this paper 
some circumstances will be mentioned, relating to the effects produced on the fasci- 
culi by the presence of chemical agents, which are only explicable on the present 
supposition, but as it would be premature to introduce them here, the same thing 
may now be proved in another way. 
It is easy for any one to satisfy himself that the fasciculi are not tubes, by the 
most decisive of all methods, the making a transverse section ; and it is strange that 
an operation so simple, which was practised by both Leeuwenhoek and Prochaska*, 
should have escaped the attention of some later inquirers. Such a section never 
presents the slightest appearance of any central cavity. I had made several trans- 
verse sections of dried fasciculi, however, before discovering in them any decided trace 
of the extremities of cut fibrillse, and concluded that in the process of drying, these 
had been so modified or united together, as to render them incapable of being indi- 
vidually distinguished ; for the addition of a little citric acid would frequently expand 
the section and give its surface a minute mottling, such as I was willing to fancy 
might depend on the structure in question. These first observations were made on 
the flesh of Mammals, and I now attribute the indistinctness of the fibrillse to their 
close and intimate lateral union, whereby they seem in this class to be generally the 
most reduced to the condition of a solid mass. But continuing to examine specimens 
derived from various sources, I was gratified by meeting at length with several which 
afforded the most ample confirmation to the views here adopted. The cut extremities 
of the fasciculi presented themselves as areas of an angular shape, more or less densely 
filled with minute dots, which are manifestly the ends of the fibrillse. In Birds more 
especially, but also in Fish and Reptiles, I have met with such appearances with great 
uniformity ; and in figs. 3 to 8. are accurate representations from each of these classes. 
The dots seem to be the extremities of solid threads. They have no central area 
distinct from their circumference, and the shadow occasioned by the image of a part 
of the window-frame in the field of the microscope, will throw one half of each of 
them into darkness. It is in this manner only that they can sometimes be brought 
into view at all. In Fish (figs. 3. 4.) the sections of the fasciculi are very ample, and 
filled up by very fine and closely-set fibrillse, presenting their extremities to the ob- 
server. Some of these fibrillse are more distinct than the rest (fig. 4.). In many 
fasciculi the fibrillse are not individually apparent, the whole surface being merely 
uniformly and finely mottled. In Reptiles (figs. 5 and 6.), the specimens exhibit more 
or less plainly the ends of the fibrillse composing the fasciculus. In Birds (fig. 7 -), the 
* Prochaska gives a figure of a transverse section of fasciculi in ■which the extremities of the fibrillae are 
seen. 
3 o 2 
