THE FASCLE AND MUSCLES OF THE TAIL ~ 279 
its course further forward the muscle receives fasciculi from the lumbar and thoracie 
spines, but diminishes somewhat in volume. About the twelfth thoracic vertebra 
it divides into two parts. The dorsal division (m. spinalis et semispinalis), rein- 
foreed by bundles from the first four thoracic spines, passes forward under the com- 
plexus to be inserted into the spines of the last four cervical vertebre. The ventral 
division passes forward and downward underneath the serratus ventralis to be in- 
serted into the ribs and the transverse processes of the last four cervical vertebre. 
Three sets of fasciculi may be distinguished, viz.: (1) spinal, which are superficial 
and medial; (2) transverse, attached to the transverse and articular processes, 
which are medial and deep; (3) costal, which are lateral. 
Relations.—Superficially, the middle gluteus, the lumbo-dorsal fascia, the 
latissimus dorsi, serrati dorsales, serratus ventralis, and complexus; deeply, the 
multifidus, intertransversales, external intercostals, levatores costarum, the liga- 
mentum nuche, and its fellow of the opposite side (in the neck). 
Blood-supply.—Dorsal, deep cervical, intercostal, and lumbar arteries. 
Nerve-supply—Dorsal branches of the thoracic and lumbar nerves. 
8. Multifidus dorsi—This is a long segmental muscle which lies along the sides 
of the spinous processes of the vertebrie from the sacrum to the neck. 
Origin.—(1) The lateral part of the sacrum; (2) the articular processes of 
the lumbar vertebr; (3) the transverse processes of the thoracic vertebre. 
Insertion —The spinous processes of the first two sacral, the lumbar, thoracic, 
and last cervical vertebrie. 
Action —Acting with its fellow, it is an extensor of the spine; acting singly, 
it flexes it laterally. 
Structure —It is composed of a series of bundles which are directed obliquely 
forward and upward. Each fasciculus passes over several vertebrz to its insertion. 
In the posterior part of the series the bundles cross two or three vertebre and are 
inserted into the summits of the spines. Anteriorly the bundles have a more 
horizontal direction, cross three to five vertebre, and are inserted into the sides 
of the spines considerably below their summits. A further complication consists 
in the fusion of several bundles into a common insertion. 
Relations—Superficially, the longissimus dorsi; deeply, the vertebral spines. 
Blood-supply.—Intercostal and lumbar arteries. 
Nerve-supply.—Dorsal branches of the thoracic and lumbar nerves. 
9. Intertransversales lumborum.—These are very thin muscular and tendin- 
ous strata, which occupy the spaces between the transverse processes of the lumbar 
vertebre except the fifth and sixth. 
Action.—To assist in flexing the loins laterally or in rendering the region rigid. 
Relations——Superficially, the longissimus dorsi; deeply, the quadratus lum- 
borum. 
Blood-supply—Lumbar arteries. 
Nerve-supply.—Lumbar nerves. 
THE FASCIA AND MUSCLES OF THE TAIL 
(FASCIA ET MUSCULI CAUDE) 
The muscles of the tail are inclosed in the strong coccygeal fascia, which is 
continuous in front with the gluteal fascia and blends with the lateral sacro-iliac 
ligament. At the root of the tail it is loosely attached to the subjacent muscles, 
but further back it is intimately adherent to them. From its deep face are de- 
tached septa which pass between the muscles to become attached to the vertebre. 
1. Coccygeus.'—This is a flat, triangular muscle which lies chiefly between the 
sacro-sciatic ligament and the rectum. 
1 Also termed the ischio-coccygeus or compressor coccygis. 
