MYOLOGY 253 
dense white fibrous tissue by means of which a muscle is attached; an aponeurosis 
is a broad fibrous sheet which fulfils a similar function. 
(4) The action belongs rather to physiological study, but the main points are 
usually given in anatomical descriptions. In some cases the action is simple, in 
others, complex. Muscles which concur in action are termed synergists; those 
which have opposite actions are antagonists. 
_ (5) The consideration of structure includes the direction of the muscular fibers, 
the arrangement of the tendons, the synovial membranes, and any other accessory 
‘structures.. The terms fleshy and tendinous are sometimes used to indicate the 
relative amounts of muscular and tendinous tissue. In the case of the long muscles 
of the.limbs, the origin is termed the head (Caput), and when the muscle is fusi- 
form, the large fleshy part is often called the belly (Venter) of the muscle. Some 
muscles have two or more heads, and are hence designated as biceps, triceps, etc. A 
digastric muscle is one having two bellies and an intermediate tendon. In most 
muscles the muscle-fibers join the tendon at an acute angle, like the relation of the 
barbs of a feather to its shaft; hence the term pennate is applied to such an arrange- 
ment. When the fibers are so arranged on one side of the tendon the muscle is 
unipennate (M. unipennatus); while one in which this arrangement exists on both 
sides is bipennate (M. bipennatus). The structure may be still more complex, re- 
sulting in a multipennate muscle. The structure of many muscles is much more 
complex than a superficial examination would lead one to suppose. Frequently 
Fibrous sheath 
Mesolencdon Fibrous sheath. 
Synoial sheath 
Fic. 260—Diacrams oF Cross-SectTIONS oF Synoviat Bursa (A) AND Synovian SHEeaTH (B); T, TENDON. 
In both the synovial sac is represented for the sake of clearness as though somewhat distended. 
they are intersected by tendinous layers or bands, known as tendinous intersec- 
tions. Intersecting bands or tracts which appear on the surface—usually as zig- 
zag |mes—are termed tendinous inscriptions (Inscriptiones tendinez). 
(6) The relations constitute a very important part of anatomical topography, 
and a knowledge of them is fundamental to further study in this respect. 
(7) The blood and nerve supply are, of course, important on clinical grounds. 
The nerve supply is often of value in the determination of homologies. As might 
be expected, the muscles have a large blood supply. They are also provided with 
lymph-yessels. The nerves to the muscles are motor, sensory, and vasomotor in 
function. 
The accessory structures associated with the muscles are the synovial mem- 
branes and the fascie. 
The synovial membranes are thin-walled sacs, similar to the synovial mem- 
branes of the joints, and having a similar function. Two forms are recognized. 
A synovial bursa (Bursa synovialis) is a simple sac which is interposed at a point of 
unusual pressure between a tendon or muscle and some underlying structure, com- 
monly a prominence of the skeleton. A synovial sheath (Vagina synovialis ten- 
dinis) differs from a bursa in the fact that the sac is folded around the tendon so that 
two layers can be distinguished: the inner one is adherent to the tendon, while the 
outer one lines the canal in which the tendon lies. The two layers are continuous 
along a fold termed the mesotendon. The arrangement is shown in the annexed 
diagrams. The synovial membranes of joints in some places form extra-articular 
