Part 30

Origin by five slips which are attached by strong tendons to the anterior articular processes of the last four cervical vertebræ. The tendons are common to this muscle and the complexus. The five slips unite to form a flat belly which has its

Insertion by a strong rounded tendon into the mastoid process of the temporal bone. The tendon may be closely united to that of the splenius.

Relations.--Lateral surface with the sternomastoid (Fig. 68, c), the levator scapulæ (Fig. 73, h), and longissimus dorsi (Fig. 69, f″). Medial surface with the splenius (Fig. 73, b) (to which it is partly united), the complexus (Fig. 69, b), and the longus atlantis (Fig. 69, d).

Action.--Lateral flexor of the head.

=M. biventer cervicis= (Fig. 69, a) (=medial portion of M. semispinalis cervicis et capitis=).--The biventer cervicis is a flat muscle which lies beneath the splenius (Fig. 73, b), next the median line of the neck, with its fibres longitudinal.

Origin in three or four slips from the surface of the three or four aponeurotic arches which take origin from the tips of the spinous processes of the last cervical and the first three thoracic vertebræ and pass laterad and caudad to the anterior processes of the second, third, fourth, and fifth thoracic vertebræ. These arches are deviated from their straight course by four aponeurotic bands which pass from them obliquely caudad and dorsad to the sides of the spinous processes of the vertebræ into which the arches are inserted. The arches form the beginning of the sheet of fascia which passes outside of the longitudinal supraspinous muscles, and the anchoring bands form the beginning of a similar sheet which passes within the longitudinal supraspinous muscles. An additional slip may take origin from the cervical ligament between the last cervical and the first thoracic vertebræ. The fibres form a flat band divided by two or three oblique tendinous intersections. It adheres closely to the cervical supraspinous ligament.

Insertion by a strong tendon into the medial part of the lambdoidal crest.

Relations.--Outer surface with the splenius (Fig. 73, b) and at the caudal end with the longissimus dorsi (Fig. 69, f″). Inner surface with the spinalis dorsi (Fig. 69, g), the semispinalis cervicis (Fig. 71, c), and the rectus capitis posterior major (Fig. 71, a). Medial edge with the muscle of the opposite side; lateral edge with the complexus (Fig. 69, b).

Action.--Raises the snout.

=M. complexus= (Fig. 69, b) (=lateral portion of M. semispinalis cervicis et capitis=).--The complexus is closely associated with the biventer cervicis (a) and lies on its lateral side beneath the splenius (Fig. 73, b).

Origin by tendinous bands from the anterior articular processes of the last five or six cervical and the first one, two, or three thoracic vertebræ. The same bands give origin externally to the fibres of the longissimus capitis (Fig. 69, e), and internally to those of deeper muscles of the neck. The six or more muscular slips continued from these tendons unite to form a flat band, the

Insertion of which is by a flat tendon into the medial third of the lambdoidal crest some distance ventrad of the free edge of the crest. Near the insertion the lateral border of the muscle is connected by an aponeurotic band to the lateral border of the transverse process of the atlas.

Relations.--Outer surface at the dorsal border with the biventer cervicis (Fig. 69, a); at the middle with the splenius (Fig. 73, b); at the ventral border with the longissimus capitis (Fig. 69, e) and the longissimus dorsi (Fig. 69, f″). Inner surface with the cervical portion of the spinalis dorsi, with the semispinalis cervicis (Fig. 71, c), the obliquus capitis inferior (Fig. 71, b), the rectus capitis posterior major (Fig. 71, a), and the obliquus superior (Fig. 71, e).

Action.--Raises the head.

=M. spinalis dorsi= extends into the cervical region; it has been described.

=M. semispinalis cervicis= (Fig. 71, c).--This represents that portion of the multifidus spinæ which extends into the cervical region. It is not composed of distinct bundles, like the multifidus of the thoracic region, but all the fibres are united into a fairly well-defined muscle.

Origin from the articular processes of the last five cervical vertebræ.

Insertion into the spinous processes of the cervical vertebræ up to the second, the largest part of the muscle being inserted into the caudal end of the spine of the atlas.

Relations.--Outer surface with the spinalis dorsi (Fig. 69, g) and the complexus (Fig. 69, b). Inner surface with the vertebræ.

Action.--Extends the neck.

=M. longissimus dorsi= extends into the cervical region, where it is often distinguished as the =longissimus cervicis= (Fig. 69, f″). It has been described.

=M. longus atlantis= (Fig. 71, f; Fig. 69, d).--This represents a differentiated portion of the longissimus dorsi.

Origin from the transverse process and the side of the vertebral arch of the third cervical vertebra.

Insertion into the caudolateral angle of the wing of the atlas.

Relations.--Dorsal surface with the complexus (Fig. 69, b), the longissimus capitis (Fig. 69, e), and the obliquus inferior (Fig. 71, b). Ventral surface with the scalenus (Fig. 71, g), longissimus dorsi (Fig. 69, f″), and levator scapulæ (Fig. 71, h).

Action.--Extends the neck and turns the head sideways.

=M. rectus capitis posterior major= (Fig. 71, a).

Origin.--The whole length of the spinous process (or crest) of the axis, or its caudal part only. It is united by a raphe to the opposite muscle. The muscle passes craniad and laterad to its