The short muscles are those in which the three dimensions are nearly
equal, having a thickness in proportion to their width and their
length. They are found in general in the places, where is required on
the one hand much power, and on the other small extent of motion; thus
around the temporo-maxillary articulation the masseter and pterygoids,
around the ischio-femoral the quadratus the gemini the obturators, &c.
around the scapulo-humeral the supra-spinalis and the teres minor,
in the hand the muscles of the palmar eminences, in the foot various
fleshy fasciculi, in the vertebral column the interspinal, in the head
the small and great anterior, posterior and lateral recti, exhibit
more or less regularly the form of which we are treating, and answer
the double object that I have indicated, on the one hand by the very
considerable number and on the other by the shortness of their fibres.
The short muscles are, more often than the broad, united to each
other, either in their origin or termination, as we see in the foot
and the hand. Sometimes they are of a triangular form, as in these two
parts; sometimes they approach to the form of a cube, of which there
is an example in the masseter and pterygoid muscles. In general they
are rarely covered by aponeuroses, undoubtedly because the shortness
of their fibres prevents them from being liable in a great degree to
considerable displacements.
Besides, the division of the muscles into long, broad and short,
is, like that of the bones, subject to an infinite number of
modifications. In fact many of these organs have mixed characters; thus
the sub-scapularis and the infra-spinalis have a form intermediate to
the broad and short one; thus the cruræus, the gemelli of the leg, &c.
cannot be considered precisely long or broad muscles. Nature varies,
according to the functions of the organs, the conformation of the
agents of their motions, and we can only establish approximations in
our anatomical divisions.