516 
arranged as a few long fibres (as in the sar- 
torius), or as many short ones (as in the 
_Tasseter). In the former case its con- 
tractions would be characterized by their ex- 
tent, in the latter by their power; for, ceteris 
paribus, the extent is as the length, the power 
as the thickness. 
The terms origin and insertion are employed 
with great convenience in ordinary anatomical 
Janguage to denote the more fixed and the more 
moveable attachments of muscles. In human 
anatomy general consent has sanctioned their 
use, and even, with few exceptions, their par- 
ticular application to each muscle in the body, 
although this assignment is in many cases arbi- 
trary, in consequence of its being impossible to 
determine which attachment is the more fre- 
quently the fixed one. 
The arrangement of the fibres in the heart 
has been already fully treated of in this work. 
(See Heart, Fibres of.) 
In the muscular coat of the alimentary canal, 
of the bladder, and uterus, the unstriped fibres 
are disposed, as in the heart, so as to enclose 
a cavity, but without having, as in that organ, 
any point at which they can be said to com- 
mence or terminate. In the alimentary tube 
they are arranged in two laminee, the respective 
fibres of which take a course at right angles to 
each other. In the bladder the arrangement is 
reticulate. The elementary fibres form sets 
of variable thickness, which at numerous 
ints send off detachments to join neigh- 
-bouring bundles, whence has sprung the notion 
that the fibres are heanghell. it is mani- 
festly, however, the sets of them only that are 
branched, the unstriped like the striped fibres 
being invariably simple from end toend. In 
the uterus the disposition of the fibres is essen- 
tially similar, calculated to allow of great 
variety in the capacity of the cavity they 
encircle. 
Of the areolar tissue of muscles-—This tissue 
is much more abundant in the voluntary than 
in the involuntary muscles. In the former it 
forms an external investment, which sends 
septa into the intervals between the larger and 
smaller packets of fibres, and thus enables 
them to move in some degree independently 
of one another. The density of these general 
and partial sheaths is proportioned to the 
amount of pressure to which the organ may be 
subject, as is exemplified in the superficial 
muscles of their back, and in those superficial 
muscles generally where a fibrous aponeurusis 
does not perform the same office. e areolar 
tissue does not usually clothe every individual 
fibre from end to end, giving it a cellular 
sheath, except in cases where the elementary 
fibres are of large dimensions. Besides the 
tection the areolar tissue affords to the mus- 
cular fibres, it admits of motions between 
them. But it must also serve the important 
office of limiting undue motions of one part 
of a muscle on another part, by its form- 
ing a connecting bond between neighbouring 
bundles. But a principal use of it appears to 
he that of furnishing a resisting nidus in which 
the delicate vessels and nerves can traverse¢ the 
MUSCLE. 
interstices of the fibres, and by which they 
can be protected from hurtful dragging during 
the unequal and oscillating movements of the 
fibres of a voluntary muscle during its state of 
activity. This idea is su ed by the fact 
that searcely any areolar tissue exists in the 
heart or in the unstriped muscles generally. — 
In the heart, though the contraction is power-— 
ful, it is instantaneous or nearly so, and there+ 
fore probably more uniformly diffased, so that 
neighbouring fibres must be less moved on one 
another than in the more sustained contraction — 
of a voluntary muscle. Moreover the mutual 
intertwining of even the elementary fibres in 
this organ is, in many parts of it, so intricate, — 
as to contribute much to their mutual support. — 
And in the other mvoluntary muscles, the con-_ 
tractions are 98 baer evenly progressive - 
along the fibres of the same set. 7 
Of the bloodvessels of muscles—The arteries 
and veins of muscles commonly run together, 
and most of the arterial branches, to within 
two removes from the capillaries, are accom- 
panied by two vene comites. invariably 
more or less across the direction of the 
fibres, divide and subdivide, first in the in- 
tervals between the larger sets, then between t 
smaller sets, till the ultimate twigs insinu 
themselves between the fibres composing the 
smallest bundles, and break up into their capil- 
lary terminations. In this course the vessel 
supply the areolar tissue, their own coats, and 
the attendant nerves. The capillary plexus of 
the areolar membrane consists of irregular 
pretty equal-sized meshes, and contrasts strong! 
with that of the muscular tissue itself. The 
proper capillaries of muscle are quite chara 
teristic in their arrangement, so that a per 
who has once seen them can never afterw: 
mistake them, They consist of longitud) 
and transverse vessels, the longitudinal alway 
following the course of the el ib 
and lying in the intervals between them, th 
transverse being short communications pla 
at nearly equal distances between the longit 
dinal ones, and crossing nearly or quite 
versely over or under the fibres. mann 
in which the longitudinal vessels are 7 
in relation to the fibres, is seen in fig. 
where I have represented them as : 
seen on a transverse section. ue 
occupy the iuterstice between three or m 
fibres, but sometimes also the space bet 
the contiguous surfaces of two fibres. “ 
length of the longitudinal vessels does 
usually exceed the twentieth of an inch; ino 
words the terminal twigs of the artery and : 
pertaining to the same aa are se 
further than that apart. length of 
transverse anastomosing capillaries neces: 
varies with the thickness of the fibres” 
which they pass (fig. 299). The diamet 
the capillaries of muscle varies like tha : 
others with the size of the blood- particles 
the animal. It is, however, only just suffiel 
to allow of the particles to pass. If a 1 ij 
ment of a frog’s oe ae fresh, | 
examined, series of blood-particles will 
seen in the longitudinal - capillaries. 
