3. =Sterno-cephalicus= (Sterno-maxillaris s.-mandibularis).[42]—This is
a long, narrow muscle, extending along the ventral and lateral aspects
of the trachea from the sternum to the angle of the jaw. It forms the
ventral boundary of the jugular furrow.
_Origin._—The cariniform cartilage of the sternum.
_Insertion._—The posterior border of the lower jaw.
_Action._—Acting together, to flex the head and neck; acting singly, to
incline the head and neck to the side of the muscle contracting.
_Structure._—The two muscles are fused at their origin, which is fleshy.
Near the middle of the neck they separate, and, becoming thinner, each
muscle passes under the parotid gland and terminates in a flat tendon.
_Relations._—Superficially, the cervical panniculus; deeply, the
sterno-thyro-hyoideus and omo-hyoideus muscles. The upper edge of the
muscle is related to the jugular vein, which lies in the jugular furrow.
The carotid artery, the vagus, sympathetic, and recurrent nerves also
lie along the upper edge at the root of the neck. The tendon passes
under the submaxillary vein and the parotid gland, having the
submaxillary gland and stylo-maxillaris muscle on its inner side.
_Blood-supply._—Carotid artery.
_Nerve-supply._—Ventral branches of the spinal accessory and first
cervical nerves.
4. =Sterno-thyro-hyoideus= (Sterno-thyroideus et sterno-hyoideus).—This
is a long, slender, digastric muscle, applied to the ventral surface of
the trachea and its fellow of the opposite side.
_Origin._—The cariniform cartilage of the sternum.
_Insertion._—(1) The external surface of the thyroid cartilage of the
larynx; (2) the body of the hyoid bone.
_Action._—To depress and retract the hyoid bone, the base of the tongue,
and the larynx, as in deglutition. It may also fix the hyoid bone when
the depressors of the tongue are acting, as in suction.
_Structure._—The origin of the muscle is fleshy, and as far as the
middle of the neck it blends with its fellow. The common belly is then
interrupted by a tendon, or sometimes two tendons, from which arise
three or four fleshy bands. The lateral bands diverge to reach their
insertion into the thyroid cartilage; while the inner bands, closely
applied to each other and blending with the omo-hyoideus, pass straight
forward to reach the ventral surface of the hyoid bone.
_Relations._—At the root of the neck the common belly has the
sterno-cephalicus below, and the carotid arteries and recurrent nerves
above. Further forward the trachea becomes the upper relation, and near
the head the skin and fascia, the lower one.
_Blood-supply._—Carotid artery.
_Nerve-supply._—Ventral branch of the first cervical nerve.
5. =Omo-hyoideus= (Subscapulo-hyoideus).—This is a thin, ribbon-like
muscle, almost entirely fleshy, which crosses the trachea very obliquely
under cover of the mastoido-humeralis.
_Origin._—The subscapular fascia close to the shoulder joint.
_Insertion._—The body of the hyoid bone, in common with the hyoid branch
of the preceding muscle.
_Action._—To depress the hyoid bone.
_Structure._—The muscle is composed of parallel fleshy fibers, except at
its origin, where it has a thin tendon.
_Relations._—In the first part of its course the muscle passes forward
between the supraspinatus, anterior deep pectoral, mastoido-humeralis
(outwardly), and the scalenus (inwardly). It is intimately adherent to
the mastoido-humeralis. In the middle of the neck it is related
superficially to the mastoido-humeralis, sterno-cephalicus, and the
jugular vein; deeply, to the rectus capitis anterior major, the carotid
artery, the vagus, sympathetic, and recurrent nerves, the trachea, and,
on the left side, the œsophagus. In its anterior part the muscle blends
with the hyoid part of the sterno-thyro-hyoideus, the two covering the
thyroid portion of the latter muscle, the thyroid gland, and the ventral
face of the larynx.
_Blood-supply._—Carotid and inferior cervical arteries.
_Nerve-supply._—Ventral branches of the cervical nerves.
6. =Scalenus= (M. scalenus primæ costæ).—This muscle is deeply situated
on the side of the posterior half of the neck. It is composed of two
parts, between which the roots of the brachial plexus of nerves emerge.
_Origin._—The anterior border and outer surface of the first rib.
_Insertion._—(1) The dorsal (smaller) portion is attached to the
transverse process of the seventh cervical vertebra; (2) the ventral
portion is attached to the transverse processes of the sixth, fifth, and
fourth cervical vertebræ.
_Action._—The neck is flexed or inclined laterally, according as the
muscles act together or singly. If the neck be the fixed point, the
muscle may have a respiratory action by pulling forward or fixing the
first rib.
_Structure._—The dorsal portion is composed of three or four fleshy
bundles.[43] The ventral portion, which is much larger, is almost
entirely fleshy, and not so divided.
_Relations._—Superficially, the anterior deep pectoral,
mastoido-humeralis, and omo-hyoideus muscles, the phrenic nerve, and the
other branches of the brachial plexus; deeply, the vertebræ, the longus
colli and intertransversales muscles, the œsophagus (on the left side),
the trachea (on the right side), the vertebral vessels, the vagus,
sympathetic, and recurrent nerves. The roots of the brachial plexus form
a flat anastomosis, which lies between the two portions of the muscle.
The brachial vessels cross the ventral edge close to the first rib.
_Blood-supply._—Carotid, vertebral, and inferior cervical arteries.
_Nerve-supply._—Ventral branches of the cervical nerves.
7. =Rectus capitis anterior major= (M. longus capitis).—This is the
largest of the three special flexors of the head, and lies along the
ventro-lateral surface of the anterior cervical vertebræ and the base of
the cranium.
_Origin._—The transverse processes of the fifth, fourth, and third
cervical vertebræ.
_Insertion._—The tubercles at the junction of the basilar process of the
occipital bone with the body of the sphenoid.
_Action._—Acting together, to flex the head; acting singly, to incline
it to the same side also.
_Structure._—The origin of the muscle is by fleshy digitations. The
belly increases in size by the union of these digitations, reaching its
maximum at the axis. It then diminishes, passes toward the median plane,
and terminates on a rounded tendon.
_Relations._—Superficially, the mastoido-humeralis, omo-hyoideus, and
rectus capitis anticus minor, the submaxillary gland, the carotid artery
(which lies along the lower border), the occipital and internal carotid
arteries, and the tenth, eleventh, and sympathetic nerves; deeply, the
vertebræ, the longus colli, intertransversales, and the small straight
muscle. The terminal part of the muscle lies in contact with its fellow
above the pharynx and between the guttural pouches.
_Blood-supply._—Carotid, vertebral, and occipital arteries.
_Nerve-supply._—Ventral branches of the cervical nerves.
8. =Rectus capitis anterior minor= (M. rectus capitis ventralis).—This
is a small muscle which lies under cover of the preceding one.
_Origin._—The ventral arch of the atlas.
_Insertion._—The basilar process, close to the preceding muscle.
_Action._—To flex the occipito-atlantal articulation.
_Structure._—Fleshy.
_Relations._—Below, to the preceding muscle; above, to the atlas,
occipito-atlantal articulation, and the basilar process; externally, to
the rectus capitis lateralis and the guttural pouch.
_Blood-supply._—Occipital artery.
_Nerve-supply._—Ventral branch of the first cervical nerve.
9. =Rectus capitis lateralis.=—This is a still smaller, entirely fleshy
muscle, which lies for the most part under the small oblique muscle.
_Origin._—The atlas, external to the preceding muscle.
_Insertion._—The paramastoid or styloid process of the occipital bone.
_Action._—The same as the preceding muscle.
_Structure_.—Fleshy.
_Relations._—Superficially, the small oblique muscle, the occipital
vessels, and the ventral branch of the first cervical nerve.
_Blood-supply._—Occipital artery.
_Nerve-supply._—Ventral branch of the first cervical nerve.
10. =Longus colli.=—This muscle covers the ventral surface of the
vertebræ, from the sixth thoracic to the atlas, and is united with its
fellow. It consists of two portions, thoracic and cervical.
_Origin._—(1) Thoracic portion, the bodies of the first six thoracic
vertebræ; (2) cervical portion, the transverse processes of the cervical
vertebræ.
_Insertion._—(1) Thoracic portion, the bodies and transverse processes
of the last two cervical vertebræ; (2) cervical portion, the bodies of
the cervical vertebræ and the tubercle on the ventral surface of the
atlas.
_Action._—To flex the neck.
_Structure._—The muscle is composed of a succession of bundles. The
largest of these constitute the thoracic part of the muscle, which has a
strong tendon inserted into the last two cervical vertebræ. A bursa is
interposed between the tendon and the spine at the first costo-vertebral
articulation. The cervical portion consists of a number of smaller
bundles, each of which passes from its origin on the transverse process
of one vertebra forward and inward to its insertion into a vertebra
further forward. The most anterior bundle is inserted by a strong tendon
into the ventral tubercle of the atlas.
_Relations._—The principal relations of the two muscles in the thorax
are: ventrally, the pleura, and, further forward, the trachea and
œsophagus; dorsally, the vertebræ and the costo-vertebral joints;
laterally, the dorsal, superior cervical, and vertebral vessels, the
sympathetic nerve, and the thoracic roots of the brachial plexus. In
the neck, important relations are: ventrally, the trachea and
œsophagus, the carotid artery, the vagus, sympathetic and recurrent
nerves; dorsally, the vertebræ and, in the middle third of the neck,
the intertransversales muscles; laterally, the scalenus, the rectus
capitis anticus major, and the intertransversales (in the anterior
third). The terminal part of the muscle is separated from the trachea
by the œsophagus, which is here median in position.
_Blood-supply._—Subcostal and vertebral arteries.
_Nerve-supply._—Ventral branches of the spinal nerves.
11. =Intertransversales colli= (Mm. intertransversarii cervicis).—These
are six fasciculi which occupy the spaces between the lateral aspects of
the vertebræ and the transverse and articular processes. There is thus a
bundle for each intervertebral articulation except the first. Each
bundle consists of a dorsal and ventral portion.
_Attachments._—The dorsal bundles pass from transverse process to
articular process; the ventral bundles extend between adjacent
transverse processes.
_Action._—To bend the neck laterally.
_Structure._—They contain strong tendinous intersections.
_Relations._—Superficially, the mastoido-humeralis, rectus capitis
anterior major, complexus, trachelo-mastoideus, splenius, scalenus, and
longissimus muscles; deeply, the vertebræ, the longus colli muscle, and
the vertebral vessels. The muscles are perforated by branches of these
vessels and by the primary branches of the cervical nerves.
_Blood-supply._—Vertebral artery.
_Nerve-supply._—The cervical nerves.