138 THE MUSCLES. 
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 
anserted by a flat tendon into the ventral surface of the caudal 
vertebrz, from the second or third to about the seventh. 
Relations.—Lateral surface with the gluteus maximus 
and abductor caude internus (Fig. 68, w). Medial surface with 
the levator ani (Fig. 162, 11), with which this muscle may be 
partly united. 
Action.—The two muscles together flex the tail. 
M. flexor caude longus (Fig. 162, 12; Fig. 113, ¢, page 
270). 
Origin on the ventral surface of the last lumbar vertebra, 
of the sacrum, and of the transverse processes of the caudal 
vertebrze. Caudad the muscle forms long, strong tendons 
which are zzserted on the ventral surface of the tail. 
Relations.—Lateral surface with the ilium, the gluteus 
maximus, the abductor caudz internus, the iliocaudalis, and the 
skin of the tail. Dorsally it touches in the caudal region the 
abductor caudz externus (Fig. 68, w), medially the flexor caudze 
brevis (Fig. 162, 13). 
Action.—Flexes the tail. 
M. flexor caude brevis (Fig. 162, 18). 
Origin on the ventral surface of the caudal vertebrz, 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 caudz longus. 
Relations—Lateral edge with the flexor caude 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. 
2. Muscles on the Ventral Side of the Vertebral Column. 
A. LUMBAR AND THORACIC REGIONS.—The iliopsoas (Fig. 
