MUSCLE. 
Trichine within the sarcolemma, from which all the 
contractile material had disappeared, 
From an Eel, 
a, ovum. 
%, worms in slow motion. 
velopment, united to form a single tube, the 
septa at first resulting from their apposition 
having been absorbed. This opinion is un- 
-doubtedly ingenious; but, as | have yet no 
data from which to judge of its correctness, 
I neither admit nor deny it. I have seen 
the sarcolemma in human muscle as early 
as the period of birth, and have traced it at 
all epochs, to old age, when the atrophy of 
its contents has often seemed to render it 
more easy of detection. It also remains in 
muscles wasted by disease or accident at other 
periods of life, and no difference appears to 
occur in it whether the specimens examined 
are pale or dark-coloured, firm or flaccid. It 
is thickest in those classes that possess the 
thickest elementary fibres, viz. in Crustacea 
and Fish, and so thin in Birds, whose fibres 
are the smallest, that it is often difficult to 
detect it at all. 
With regard to the use which this singular 
structure may serve in the economy of the 
organ, our present ignorance of the manner in 
which motion is excited renders any explana- 
tion that might be offered of doubtful value. 
But it has appeared probable to me, first, that 
it may act as a mechanical protector and iso- 
lator of the contractile tissue enclosed within it; 
secondly, that its exquisitely smooth exteraal 
‘surface may facilitate those rapid minute 
motions of neighbouring fibres, one against 
another, which may be shown to og¢cur in 
contracting muscle (see Muscutar Motion); 
and, thirdly, that from its apparent similarity 
in structure to the membrane of the neryous 
tubules, which run among the fibres, and be- 
tween which and the proper contractile tissue 
it seems certainly to intervene, as well as 
from its extensive contact and union with 
the surface of the contractile tissue, it may be 
the conducting medium of that influence, 
“whose mode of propagation the late disco- 
_very of the loop-like termination of the nerves 
in muscle has hitherto only seemed to render 
more inexplicable than ever. 
fir Of the extremities of the elementary 
res, and their attachment to other struc- 
ures.—Every fibre is fixed to fibrous tissue, or 
to something analogous to it; but an accurate 
€xamination of this difficult subject gives no 
‘countenance to the ordinarily received opinion 
‘that this tissue is prolonged over the whole fibre 
from end to end, as its cellular sheath; nor is 
this view reconcileable with the physical require- 
ments of the case. After many trials I have 
hever succeeded in isolating a muscular fibre 
with the tendinous fibrille pertaining to it, in 
ther Mammalia or Birds; but this may be 
VOL, III. : 
513 
oceasionally accomplished in Fishes, and in 
certain muscles of insects. In these examples 
the minute detachment of the fibrous tissue 
may be seen to pass and become attached to 
the truncated extremity of the fibre. The fibre 
ends by a perfect disc, and with the whole 
surface of this disc the tendon is connected 
and continuous (fig. 297). The sarcolemma 
Fig. 297. 
Extremity of an elementary fibre, from the Skate 
( Raia Batus), shewing its attachment to tendon. 
a, a, line of union between the two structures, 
b, tendon. ! 
ec, muscle. 
ceases abruptly at the circumference of the 
terminal disc, and here some small part of the 
tendinous material appears to ‘be joined to it. 
The same disposition may be well seen in the 
legs of certain insects (fig. 293). In other 
cases, where the muscle is fixed obliquely to 
a membranous surface, each fibre is obliquely 
truncated at its extremity, at an angle deter- 
mined by the inclination of its axis, instances 
of which may be seen in the limbs of Crus- 
tacea, and elsewhere. 
9. Development.—The researches of Valentin 
and Schwann have shewn that a muscle con- 
sists in the earliest stage of a mass of nu- 
cleated cells, which first arrange themselves in 
a linear series, with more or less regularity, 
and then unite to constitute the elementary 
fibres. As this process of agglutination of the 
cells is going forward, a deposit of contractile 
material gradually takes place within them, 
commencing on the inner surface and ad- 
vancing towards the centre, till the whole is 
solidified. The deposition occurs in granules, 
which, as they come into view, are seen to be 
disposed in the utmost order, according to the 
two directions already so often mentioned. 
These granules are the sarcous elements, and 
being of the same size as in the perfect muscle, 
the transverse stripes resulting from their appo- 
sition are of the same width as in the adult; 
but as they are very few in number, the fibres. 
which they compose are of corresponding 
tenuity. From the very first period of their for- 
mation these granules are parts of a mass and 
not independent of one another, for as soon 
as solid matter is depgsited in the cells, faint 
2k 
