MUSCLES OF THE BODY. 129 
partly separated bundles, each with an oblique tendon. The 
muscle begins at the last or next to the last rib, where it is 
connected with the longissimus by a rather small bundle of 
fibres. The rest of the muscle-fibres take origin in bundles 
from the lateral surface of the ribs, at about the angles, or from 
thin tendons connecting the angles, of the ribs; they pass 
obliquely craniad and are inserted, usually by tendons, on the 
lateral surface of the third or fourth rib craniad of the one on 
which the given bundle has origin. The insertions on any 
given rib lie ventrad of the origins on the same rib, In the 
cat this muscle is confined to the thoracic region. 
Relations.—Outer surface with the serratus posterior inferior 
(Fig. 73, 2) and superior (Fig. 73, 7), and the levator scapulz 
(Fig. 73, #). Inner surface with the dorsal surface of the ribs, 
the external intercostals (Fig. 69, 2), and craniad with the 
levatores costarum. Medial edge in contact with the longissi- 
mus dorsi (Fig. 60, 7’). 
Action. —Draws the ribs together. 
M. spinalis dorsi (Fig. 69, g).—A muscle interconnecting 
the spinous processes of vertebrze some distance apart, in the 
thoracic and cervical regions. It lies on the medial side of the 
longissimus dorsi (/’). 
Origin by strong tendons from the tips of the spinous pro- 
cesses of the tenth to the thirteenth thoracic vertebrae. These 
tendons represent the cranial portion of the deep layer of the 
lumbodorsal fascia, and give origin also to many fibres of the 
longissimus dorsi, so that the two muscles are completely 
united at the origin of the spinalis. They become separated at 
about the level of the sixth thoracic vertebra, the spinalis form- 
ing a strong separate bundle passing into the neck region close 
against the sides of the spinous processes. The insertion is by 
fleshy bundles into the sides of the spinous processes of the first 
nine or ten thoracic vertebrz and of the cervical vertebra as 
far forward as the second. Some of the fibres of this muscle 
pass craniad into the biventer cervicis (Fig. 69, a). 
Relations.—Outer surface with the tendons of the serratus 
posterior inferior (Fig. 73, m2) and serratus posterior superior 
(Fig. 73, 7), and with the splenius (Fig. 73, 4), biventer 
