476 
MR. BOWMAN ON THE MINUTE STRUCTURE AND 
This structure can usually be seen best in specimens prepared when recent, but I 
have preparations which show it perfectly preserved in parts long - steeped in spirit. 
From its extreme tenuity, it would hardly be likely to attract any attention, were it 
not that, without extraordinary care, it is apt to be detached in different ways from the 
bundle invested by it, and so to become an isolated object. But when its existence 
is known, it may often be discovered in unbroken fasciculi, as observed by Muller, 
under the form of a straight linear margin, uninterrupted, and independent of the 
striae ; which, however, will very probably seem at first to pass completely across, 
though they terminate, in fact, within this edge. Some accurate observers have 
doubted the prominence of the beads of the fibrillae, because they have been unable 
to see their bulge at the extreme edge of the fasciculus, a circumstance which may 
depend on the existence of this sheath. 
It may also be frequently seen encircling the areas of fasciculi in the transverse 
sections of dried muscle (fig. 7- «•)> but the readiest and most satisfactory manner of 
demonstrating it, is to take the fresh muscle of a fish or reptile, and by seizing single 
fasciculi by one of their extremities, to pull them from the mass. In this operation 
they undergo considerable stretching, and often break entirely across. But such 
fractures will vary in extent, and so display the sarcolemma, for this is more extensile 
than the fibrillae inclosed in it, and therefore, where these have given way, it often re- 
mains entire, investing both fragments, and connecting them together. In such a case 
the severed extremities of the fibrillae have been pulled asunder within the sheath, and 
a tubular portion of it, containing a little of the water in which the specimen is placed, 
extends from one to the other (figs. 32 to 36 .). The sides of this, as might be anti- 
cipated, are not in focus at the same time, but they have a tendency to fall together, 
and do so more or less according to their length, and the amount of extension con- 
tinued to be applied to the fasciculus. The extremities of the tube always pass to 
the margins of the fasciculus at its broken part, and embrace it, becoming continuous 
with its transparent edges, already spoken of. If one of the fragments be turned or 
twisted, the parietes of the tube are twisted likewise, and thrown into wrinkles, which 
are most readily visible under the miscroscope, and evince the wonderful tenuity as 
well as firmness of the tissue. It not unfrequently happens that the fasciculus has given 
way at several points, and yet its sheath escaped untorn; the consequence of which is 
that the broken fragments, more or less deranged according to their size, lie in 
disorder and turned in various directions within the sheath, which still serves to keep 
them together, and may be discerned stretching from piece to piece, inclosing and 
embracing them all (fig. 36 .). These tubular bridges are sometimes more than six 
u. Pflanzen, p. 165.), speaking of the development of voluntary muscle, describes, with considerable accuracy, 
the membrane here spoken of ; and to him its discovery is really due, which I am glad to have an opportunity of 
acknowledging. He has seen it forming a transparent border to the fasciculi, as well as connecting detached 
fragments of them, but in Insects and Fish only (see his Plate IV. figs. 4, 5.), and he ingeniously supposes it 
to be a persistent portion of the membrane of the original cells of development, united to form a single tube.] 
