150 THE MUSCLES. 
Action.—Assists the serratus posterior superior. 
M. transversus costarum, or sternocostalis externus 
(Fig. 73, 7).—This is a thin muscle applied to. the cranial part 
of the side of the thorax, covering the cranial end of the rectus 
abdominis (£). 
Origin by tendon from the side of the sternum between the 
attachments of the third and sixth ribs. The muscle passes 
dorsocraniad to its 
dnsertion on the first rib and the lateral portion of its costal 
cartilage. : 
Relations. —Outer surface with the pectoralis minor (Fig. 
65, 0). Inner surface with the scalenus (Fig. 73, /’”), the 
rectus abdominis (Fig. 73, %), and the intercostales externi 
(Fig. 73, m). Atits insertion it is united with a portion of the 
scalenus (Fig. 73, 7’). 
Action.—Draws the sternum forward. 
Mm. levatores costarum.— Small muscles having origin 
on the transverse processes of the thoracic vertebra, passing 
caudoventrad, and ‘becoming zzserted on the angle of the rib 
lying immediately caudad of the origin. They are continuous 
with the external intercostals. 
Relations.—Outer surface with the longissimus dorsi (Fig. 
69, 7), and craniad with the iliocostal (Fig. 69, 2). Inner 
surface with the internal intercostals (Fig. 69, &). 
Action.—Pull the ribs dorsocraniad. 
Mm. intercostales externi (Fig. 73, ; Fig. 69, 7).—The 
external intercostals are placed in the outer portion of the 
intercostal spaces. They are composed of bundles of fibres 
attached by their ends to the adjacent borders of the ribs and 
having in general the direction of the external oblique muscle, 
i.e., they pass from their cranial ends caudoventrad. They 
occupy the intercostal spaces between the true ribs and extend 
even caudad into the spaces between the false ribs. They are 
lacking between the ventral ends of the costal cartilages of the 
first six to eight ribs, so that the internal intercostals (Fig. 
69, #) are here exposed. The more caudal external intercos- 
tals are more nearly craniocaudal in direction. 
Relations.— Outer surface with obliquus abdominis externus 
