Sacrospinalis is a very thick, lateral portion of an epaxial muscle in
mammals which continues anteriorly up to the neck and divides into three
muscles: semispinalis, longissimus, and iliocostalis. Its origin is on the
spines of the last four thoracic vertebrae, and its insertion is on both the
spines of the most craniad thoracic vertebrae and the cervical vertebrae. Its
action is to extend the vertebral column.
The semispinalis is the muscle immediately lateral to the
multifidus spinae and is the most medial of all three. It consists of
The longissimus is the muscle lateral to the semispinalis. It is the longest
subdivision of the sacrospinalis that extends forward into the transverse
processes of the posterior cervical vertebrae.
The iliocostalis is the muscle immediately lateral to the longissimus that is
the nearest to the furrow that separates the epaxial msucles from the hypaxial.
It lies very deep to the fleshy portion of the
Details From Gray's Anatomy
The Sacrospinalis (Erector spinæ), and its prolongations in the thoracic and
cervical regions, lie in the groove on the side of the vertebral column. They
are covered in the lumbar and thoracic regions by the
lumbodorsal fascia, and in the cervical region by the nuchal fascia. This
large muscular and tendinous mass varies in size and structure at different
parts of the vertebral column. In the sacral region it is narrow and pointed,
and at its origin chiefly tendinous in structure. In the lumbar region it is
larger, and forms a thick fleshy mass which, on being followed upward, is
subdivided into three columns; these gradually diminish in size as they ascend
to be inserted into the vertebræ and ribs.
The Sacrospinalis arises from the anterior surface of a broad and thick
tendon, which is attached to the medial crest of the sacrum, to the spinous
processes of the lumbar and the eleventh and twelfth thoracic vertebræ, and the
supraspinal ligament, to the back part of the inner lip of the iliac crests and
to the lateral crests of the sacrum, where it blends with the sacrotuberous and
posterior sacroiliac ligaments. Some of its fibers are continuous with the
fibers of origin of the Glutæus maximus. The muscular fibers form a large fleshy mass which splits,
in the upper lumbar region into three columns, viz., a lateral, the Iliocostalis,
an intermediate, the Longissimus, and a medial, the Spinalis. Each of these
consists from below upward, of three parts, as follows:
The Iliocostalis lumborum (Iliocostalis muscle; Sacrolumbalis muscle)
is inserted, by six or seven flattened tendons, into the inferior borders of the
angles of the lower six or seven ribs.
The Iliocostalis dorsi (Musculus accessorius) arises by flattened
tendons from the upper borders of the angles of the lower six ribs medial to the
tendons of insertion of the
Iliocostalis lumborum; these become muscular, and are inserted into the
upper borders of the angles of the upper six ribs and into the back of the
transverse process of the seventh cervical vertebra.
The Iliocostalis cervicis (Cervicalis ascendens) arises from the
angles of the third, fourth, fifth, and sixth ribs, and is inserted into the
posterior tubercles of the transverse processes of the fourth, fifth, and sixth
The Longissimus dorsi is the intermediate and largest of the
continuations of the Sacrospinalis. In the lumbar region, where it is as yet
blended with the Iliocostalis lumborum, some of its fibers are attached to the
whole length of the posterior surfaces of the transverse processes and the
accessory processes of the lumbar vertebræ, and to the anterior layer of the
lumbodorsal fascia. In the thoracic region it is inserted, by rounded tendons,
into the tips of the transverse processes of all the thoracic vertebræ, and by
fleshy processes into the lower nine or ten ribs between their tubercles and
The Longissimus cervicis (Transversalis cervicis), situated medial to
the Longissimus dorsi, arises by long thin tendons from the summits of the
transverse processes of the upper four or five thoracic vertebræ, and is
inserted by similar tendons into the posterior tubercles of the transverse
processes of the cervical vertebræ from the second to the sixth inclusive.
The Longissimus capitis (Trachelomastoid muscle) lies medial to the
Longissimus cervicis, between it and the Semispinalis capitis. It arises by
tendons from the transverse processes of the upper four or five thoracic
vertebræ, and the articular processes of the lower three or four cervical
vertebræ, and is inserted into the posterior margin of the mastoid process,
beneath the Splenius capitis and Sternocleidomastoideus. It is almost always crossed by a tendinous
intersection near its insertion.
The Spinalis dorsi, the medial continuation of the Sacrospinalis, is
scarcely separable as a distinct muscle. It is situated at the medial side of
Longissimusdorsi, and is intimately blended with it; it arises by three or
four tendons from the spinous processes of the first two lumbar and the last two
thoracic vertebræ: these, uniting, form a small muscle which is inserted by
separate tendons into the spinous processes of the upper thoracic vertebræ, the
number varying from four to eight. It is intimately united with the Semispinalis
dorsi, situated beneath it.
The Spinalis cervicis (Spinalis colli) is an inconstant muscle, which
arises from the lower part of the
ligamentum nuchæ, the spinous process of the seventh cervical, and sometimes
from the spinous processes of the first and second thoracic vertebræ, and is
inserted into the spinous process of the axis, and occasionally into the spinous
processes of the two vertebræ below it.
The Spinalis capitis (Biventer cervicis) is usually inseparably
connected with the