On the dorsal
aspest of the fore-limb, as of the hind-limb, certain muscles
arise in part from the arch, and, in part, from the bone of the
proximal segment of the limb, and go to be inserted into the
two bones of the second segment. These are, in the forelimb,
the
triceps extensor and the
supinator brevis; in the
hind-limb, the
quadriceps extensor.
There is this difference between these two homologous
groups of muscles - that in the fore-limb, the principal mass
of the muscular fibres goes, as the
triceps, to be inserted into
the post-axial bone (ulna), and the less portion, as
supinator brevis,
into the pre-axial bone (radius); whereas, in the hindlimb,
it is the other way, almost the whole of the muscular
fibres passing, as the
quadriceps, to the pre-axial bone (tibia),
the tendon commonly developing a sesamoid
patella; while
only a few fibres of that division of the quadriceps which is
called the "
vastus externus" pass to the post-axial bone
(fibula).
On the ventral aspect, the fore-limb presents three muscles,
arising either from the pectoral arch, or from the humerus,
and inserted into the two bones of the forearm. On the
pre-axial side are two muscles; one double-headed, the
biceps,
arising from the scapula and the coracoid, and inserted into
the radius. A second, the
supinator longus, passes from the
humerus to the radius. On the post-axial side, the
brachialis
anticus arises from the humerus, and is inserted into the ulna.
The hind-limb has two muscles, the
sartorius, arising from the
ilium, and the
gracilis, from the pubis, in place of the
biceps
brachii, and inserted into the pre-axial bone, the tibia, which
corresponds with the radius. Two other muscles, the
semi-membranosus and
semi-tendinosus, pass from the ischium to
the tibia, and replace, without exactly representing, the
supiinator longus.
Corresponding with the
brachialis anticus is the short head of the
biceps femoris, arising from the femur,
and inserted into the post-axial bone of the leg, the fibula.
The long head of the
biceps femoris, which proceeds from the
ischium, appears to have no representative in the fore-limb.
In the fore-limb, a muscle, the
pronator teres, passes obliquely fiom the post-axial condyle of the humerus to the radius,
in the hind-limb, a corresponding muscle, the
poplitanous proceeds from the post-axial condyle of the femur to the tibia.
The
pronator quadnitas, which passes from the ulna to the
radius, has its analogue, in some
Marsupialia and
Reptilia,
in muscles which extend from the fibula to the tibia.