Mm. interspinales.—Muscle-bundles passing from the spinous process of one vertebra to that of the vertebra immediately craniad or caudad of it. They are best developed in the lumbar region.
Mm. intertransversarii.—Muscle-fibres interconnecting the transverse processes. In the lumbar region the intertransversarii mediales connect the accessory and mammillary processes; the intertransversarii laterales lying between the transverse processes. In other regions only one set of the intertransversarii is to be distinguished.
(b) Dorsal Muscles of the Cervical Region.
—The clavotrapezius ([Fig. 68], d) and occipitoscapularis ([Fig. 73], a) have been described in connection with the muscles of the [shoulder]. The remaining muscles of this region may be considered as differentiations of the general vertebral musculature (M. extensor dorsi communis).
M. splenius ([Fig. 73], b.)—A large sheet of muscle covering the dorsal part of the side of the neck, beneath the trapezii.
Origin from the whole cervical ligament and from the fascia covering the deeper muscles along a line which extends from the first thoracic spinous process caudolaterad for about two centimeters.
Insertion by a thin tendon into the whole lambdoidal ridge. Laterad the tendon may be fused with that of the longissimus capitis ([Fig. 73], g).
Relations.—Outer surface with the sternomastoid ([Fig. 68], c), occipitoscapularis ([Fig. 73], a), clavotrapezius ([Fig. 68], d), rhomboideus, tendon of the serratus posterior superior ([Fig. 73], l), and the levator scapulæ ([Fig. 73], h). Lateral edge closely united with the longissimus capitis ([Fig. 73], g). Inner surface with the longissimus capitis, complexus ([Fig. 69], b), and biventer cervicis ([Fig. 69], a).
Action.—Lateral flexor of the head. The two together elevate the head.
M. longissimus capitis (trachelomastoideus) ([Fig. 73], g; [Fig. 69], e).—This is a slender muscle lying close against the lateral border of the splenius ([Fig. 73], b), and sometimes fused with the splenius at its craniad end. It is a cranial continuation of the longissimus dorsi ([Fig. 69], f″).