Action.—The two muscles together flex the tail.
M. flexor caudæ longus ([Fig. 162], 12; [Fig. 113], c, [page 270]).
Origin on the ventral surface of the last lumbar vertebra, of the sacrum, and of the transverse processes of the caudal vertebræ. Caudad the muscle forms long, strong tendons which are inserted on the ventral surface of the tail.
Relations.—Lateral surface with the ilium, the gluteus maximus, the abductor caudæ internus, the iliocaudalis, and the skin of the tail. Dorsally it touches in the caudal region the abductor caudæ externus ([Fig. 68], w), medially the flexor caudæ brevis ([Fig. 162], 13).
Action.—Flexes the tail.
M. flexor caudæ brevis ([Fig. 162], 13).
Origin on the ventral surface of the caudal vertebræ, from the first to the seventh or eighth. The principal head comes from the first vertebra. The bundles thus formed pass caudad and are inserted each into the ventral surface of a vertebra some distance caudad of the origin. The muscle extends to about the tenth caudal vertebra, and its most caudal parts are closely interconnected with the flexor caudæ longus.
Relations.—Lateral edge with the flexor caudæ longus. Medial edge in the sacral region with the levator ani ([Fig. 162], 11) and the iliocaudalis ([Fig. 162], 11′); in the caudal region with the muscle of the opposite side.
Action.—Flexes the tail.