Insertion into the lumbar spinous processes and the intervening interspinous ligaments.
Relations.—Outer surface with the latissimus dorsi ([Fig. 68], p), and at the origins with the intercostales externi ([Fig. 73], m). Inner surface with the intercostales interni ([Fig. 69], k) at the origin and with the intercostales externi ([Fig. 69], i), iliocostal ([Fig. 69], h), longissimus dorsi ([Fig. 69], f), and the caudal end of the spinalis dorsi ([Fig. 69], g).
[Fig. 73].—Body Muscles exposed after Removal of the Forelimb and the Muscles shown in [Fig. 68].
![[Fig. 73]](#3418956513767812439_illo149lg.jpg.id-1103802261998330825.wrap-0.html.html){kind=link}
a, M. occipitoscapularis (cut); b, M. splenius; c, M. levator scapulæ ventralis (cut); d, M. cleidomastoideus (cut); e, M. longus capitis; f, M. scalenus (f′, middle division; f″, dorsal division; f‴, ventral division; f, cervical portion); g, M. longissimus capitis; h, M. levator scapulæ (cut); i, M. serratus anterior (cut); j, M. transversus costarum; k, M. rectus abdominis (k′, its tendon); l, M. serratus posterior superior; m, M. intercostales externi; n, M. serratus posterior inferior; o, M. obliquus abdominis internus; p, lumbodorsal fascia.
Action.—Assists the serratus posterior superior.
M. transversus costarum, or sternocostalis externus ([Fig. 73], j).—This is a thin muscle applied to the cranial part of the side of the thorax, covering the cranial end of the rectus abdominis (k).
Origin by tendon from the side of the sternum between the attachments of the third and sixth ribs. The muscle passes dorsocraniad to its
Insertion on the first rib and the lateral portion of its costal cartilage.
Relations.—Outer surface with the pectoralis minor ([Fig. 65], o). Inner surface with the scalenus ([Fig. 73], f‴), the rectus abdominis ([Fig. 73], k), and the intercostales externi ([Fig. 73], m). At its insertion it is united with a portion of the scalenus ([Fig. 73], f‴).