MOVEMENTS OF VOLUNTARY MUSCLE. 
459 
glass descends, the obliquity of the surfaces may be ascertained by the more or less 
rapid extension of the field of vision on either side; and if irregularities occur in this 
respect, they can depend on no other cause than a varying inclination of the surfaces, 
or, in other words, on angularities of the fasciculus, and this circumstance I have 
uniformly remarked. Although the cut extremities of recent fasciculi are usually 
bruised and distorted by the edge of the instrument employed, I have sometimes ac- 
cidentally obtained one, which, from the sharpness of its outline, seemed fairly to 
represent the real figure of the fasciculus, and this figure has been polygonal. On 
one occasion also, when examining muscle that had been macerated in liquor ammo- 
nia, the section shown in Plate XVI. fig. 1. presented itself, which is the best of the 
kind I have met with in a wet specimen. On the whole, my examinations of recent 
specimens sanction the opinion that the fasciculi are in general far from being cylindri- 
cal, though occasionally approaching very nearly to that configuration. 
It may be said, that the appearances above described are referrible to violence done 
to the soft and delicate texture of the fasciculus by the act of detaching it from the 
mass, but their constancy has convinced me that such is not the case ; and indeed 
the form contended for is well designed for package, and is probably determined by 
the mutual pressure of parts, which have been formed and have increased together. 
But the most conclusive evidence in favour of the polygonal form of the fasciculi, 
is to be obtained by examining a transverse section of a dried muscle, after causing 
it to reassume its original bulk by wetting it*. In such examples the fasciculi are, 
without any exceptions, found to be not cylindrical, but more or less flattened on 
several of their aspects, where they are in contact with the neighbouring ones, and 
this so irregularly, that it would be in vain to attempt a particular description of 
their forms. An idea will be best, conveyed by a reference to the illustrations (fig. 3 
to 8.), in which it will be seen that the sections present almost every variety of figure 
that can be inclosed by from three to six or more sides. In some examples, most of 
the angles are sharp and decided, while others are rounded off, so as to leave spaces 
between the contiguous fasciculi, often for the passage of vessels. In other instances, 
most, or all of the fasciculi have the angles so much rounded, that they are not very 
much removed from the cylindrical shape. These are by far the least common, and I 
have only met with them in birds. In insects, the fasciculi are often flattened bands. 
(Fig. 2. Staghorn Beetle.) 
The primitive fasciculi vary considerably in bulk in different classes and genera of 
animals, and even in the same animal and the same muscle. In the course of my 
inquiry I have noted down the average diameter of the fasciculi in the specimens 
examined ; and in the following Table, examples of these measurements are exhibited. 
It is to be observed, that where the admeasurement is single, it is an average of many, 
and two numbers denote the extremes met with. 
* This plan was long ago adopted by Leeuwenhoek and Pkochaska, as well as by others. 
3 n 2 
