Origin from the lateral border of the transverse process of the atlas on its ventral margin. The fibres pass craniad and diverge.
Insertion into the caudal side of the mastoid process of the temporal bone and into a line parallel with the lambdoidal ridge and ventrad of it, from the mastoid process to within one centimeter of the median line.
Relations.—Outer surface with the splenius ([Fig. 73], b), complexus ([Fig. 69], b), and longissimus capitis ([Fig. 73], g). Inner surface with the obliquus inferior ([Fig. 71], b), the wing of the atlas, and the rectus lateralis ([Fig. 72], d). Ventral border with the cleidomastoid ([Fig. 73], d) and one head of the levator scapulæ ventralis ([Fig. 72], c′).
Action.—Flexes the head laterally.
Mm. interspinales and intertransversarii are found in the neck region also; they are described with the muscles of the [back].
C. Muscles of the Tail.
—M. extensor caudæ medialis ([Fig. 70], e).—This is a continuation caudad of the multifidus spinæ ([Fig. 70], d); it lies next to the dorsal median line, the muscles of right and left side touching one another in the middle line.
Origin by numerous fleshy bundles from the spinous processes of the sacral and first caudal vertebræ. The fibres pass caudad and are inserted by tendons into the articular processes and the dorsal surface of the caudal vertebræ.
Action.—Extends (raises) the tail.
M. extensor caudæ lateralis ([Fig. 70], f).—This is a continuation caudad of the medial portion of the longissimus dorsi ([Fig. 70], a); it lies just laterad of the extensor caudæ medialis ([Fig. 70], e).