Origin in many fleshy bundles from the articular processes of the sacral vertebræ, and the transverse processes of the caudal vertebræ. The fibres curve dorsocaudad and are inserted by many long slender tendons on the dorsal surfaces of the caudal vertebræ. The muscle grows continually smaller as it passes caudad.
Action.—Raises the tail.
M. abductor caudæ (coccygis) externus ([Fig. 68], w; [Fig. 70], g).—A rounded muscle on the lateral surface of the cranial part of the tail.
Origin from the medial side of the dorsal border of the ilium, and from the dorsal surface of the sacrum. The muscle passes caudad, lying just ventrad of the extensor lateralis, and is inserted into the transverse processes and lateral surfaces of the caudal vertebræ, as far back as the eighth or ninth.
Action.—Bends the tail sideways.
M. abductor caudæ internus (or M. coccygeus).—A large flat muscle, having origin on the spine of the ischium. The muscle passes dorsomediad, spreading out, and is inserted into the transverse processes of the second to the fourth caudal vertebræ.
Relations.—Lateral surface with the caudofemoralis ([Fig. 68], s), gluteus maximus, and pyriformis. Medial surface with the iliocaudalis and the flexor caudæ longus ([Fig. 68], x).
M. iliocaudalis (Str.-D.) ([Fig. 162], 11′, [page 398]).—This represents a portion of the levator ani of man, and in some specimens is united with that muscle ([Fig. 162], 11) in the cat.
Origin along the ventral half of the medial surface of the ilium, caudad of the sacrum. The fibres pass caudad and are inserted by a flat tendon into the ventral surface of the caudal vertebræ, from the second or third to about the seventh.
Relations.—Lateral surface with the gluteus maximus and abductor caudæ internus ([Fig. 68], w). Medial surface with the levator ani ([Fig. 162], 11), with which this muscle may be partly united.