(=a=) =Rhomboideus cervicalis s. cervicis.=—_Origin._—The funicular
portion of the ligamentum nuchæ, from the second cervical to the second
thoracic vertebra.
_Insertion._—The internal surface of the cartilage of the scapula.
(=b=) =Rhomboideus thoracalis s. dorsalis.=—_Origin._—The spinous
processes of the second to the seventh thoracic vertebra by means of the
dorso-scapular ligament.
_Insertion._—The inner surface of the cartilage of the scapula.
_Action._—To draw the scapula upward and forward. When the limb is fixed
the cervical portion will elevate the neck.
_Structure._—The cervical portion is narrow, pointed at its anterior
extremity, and lies along the funicular part of the ligamentum nuchæ, to
which it is attached by short tendon bundles. The fibers are directed
for the most part longitudinally. The thoracic portion is quadrilateral
in shape, and its fibers are nearly vertical. Its deep face is
intimately attached to the dorso-scapular ligament.
_Relations._—Superficially, the skin and fascia (over a small area), the
trapezius, and the cartilage of the scapula; deeply, the dorso-scapular
ligament, the splenius, complexus, longissimus dorsi, and serratus
anticus.
_Blood-supply._—Dorsal and superior cervical arteries.
_Nerve-supply._—Sixth cervical nerve.
3. =Latissimus Dorsi.=—This is a wide muscle which has the form of a
right-angled triangle. It lies for the most part under the skin and
panniculus, on the lateral wall of the thorax, from the spine to the
arm.
_Origin._—The lumbo-dorsal fascia—and by this means from the lumbar and
thoracic spines as far forward as the highest point of the withers.
_Insertion._—The internal tubercle of the humerus, in common with the
teres major.
_Action._—To draw the humerus upward and backward and flex the shoulder
joint. If the limb is advanced and fixed, it draws the trunk forward.
_Structure._—The muscle arises by a wide aponeurosis, which fuses with
that of the serratus posticus and with the lumbo-dorsal fascia. The
muscular portion is at first rather thin, but by the convergence of its
fibers becomes thicker as it approaches the arm. The anterior fibers
pass almost vertically downward over the dorsal angle of the scapula and
its cartilage. The posterior fibers are directed downward and forward.
The thick belly formed by the convergence of these passes under the
triceps to end on the flat tendon of insertion, which is common to this
muscle and the teres major.
_Blood-supply._—Subscapular, intercostal, and lumbar arteries.
_Nerve-supply._—Brachial plexus (eighth cervical and dorsal roots).