Page 160 - Anatomy and Physiology of Farm Animals, 8th Edition

Anatomy of the Muscular System / 145

within it) are arranged in fascicles that run can be referred to as the m. erector spinae.
Epaxial muscles are innervated by the dor­
longitudinally, transversely, and vertically,
VetBooks.ir allowing the tongue to change shape in sal branches of spinal nerves in a segmental
fashion (i.e., individual muscle fascicles are
multiple planes. Extrinsic muscles of the
tongue, those that attach outside the innervated by branches of the spinal nerves
tongue, include the m. genioglossus, which that are closest to them).
arises from the rostral part of the mandible The epaxial muscles form long columns,
(the genu) and inserts in the base of the parallel to the vertebral column and attach­
tongue so that its contraction draws the ing to the vertebrae, ilium (in the lumbar
entire tongue rostrad. The m. hyoglossus region), ribs (in the thorax), and skull (in
arises from the hyoid apparatus and inserts the neck) (Fig. 7‐14). Their position dorsal
in the base of the tongue; it draws the to the transverse process means that these
tongue caudad. The m. mylohyoideus lies muscles are responsible for extension and,
transversely between the rami of the man­ when acting unilaterally, lateral flexion of
dible. It is not, therefore, strictly a muscle the vertebral column. They may also cause
of the tongue, but its contraction lifts the rotation (twisting) of the vertebral column,
floor of the mouth, and hence the tongue, as seen when a bucking horse throws the
pressing it against the roof of the mouth. front feet to one side and hind feet to the
opposite side.
The epaxial muscles closest to the spines
Muscles of the Trunk and Neck of the vertebrae are collectively part of the
transversospinalis system. This includes
Extensors of the Vertebral Column many specifically named muscles that act
directly on the joints between vertebrae.
The group of muscles dorsal to the trans­ Fibers of these muscles typically span one
verse processes of the vertebrae on either or a few vertebrae from transverse to
side of the spinous processes are the epax- spinous processes.
ial muscles (Fig. 7‐13). Collectively, they Lateral to this is the largest (in both
mass and length) of the epaxial muscles,
the m. longissimus, parts of which extend
from the skull to the sacrum. It is composed
of many small bundles of muscle fibers that
extend from vertebral transverse processes
a to spinous processes, from transverse pro­
cesses to transverse processes, or between
a’ spinous processes. These attachments may
b extend from one vertebra to the next or
overlap one or more vertebrae.
c
Most lateral is the iliocostalis system,
characterized by distinctive tendinous
bands connecting it to the ribs and a broad
fascial attachment in the lumbar region.
The same general arrangement of
epaxial muscles is continued into the neck,
Figure 7-13. Cross‐sectional schematic of where additional muscles contribute to
epaxial muscle systems. By definition, these mus­ the flexibility of head movements. The
cles are dorsal to the transverse processes of the
vertebrae (dashed line). There are three main most superficial of these muscles is the
groups: a, transversospinalis system (including a’, m. splenius, and deep to it is the m. semi-
mm. multifidi); b, longissimus system; c, iliocosta­ spinalis capitis, which is a continuation of
lis system. the transversospinalis system in the neck