MUSCLES OF THE BODY. \2(y 



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 orij^nn in bundles 

 fi-om 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 

 (I^ig- 73. ^0 ^"<^ superior (Fig. Ji, /), and the levator scapulae 

 (i''b- 7Z^ ^O- Inner surface with the dorsal surface of the ribs, 

 the external intercostals (Fig. 69, z), and craniad with the 

 levatores costarum. Medial edge in contact with the longissi- 

 mus dorsi (Fig. 69, f). 



Action. — Draws the ribs together. 



M. spinalis dorsi (Fig. 69, g). — A muscle interconnecting- 

 the spinous processes of vertebrae 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 vertebras. 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 vertebras and of the cervical vertebrae 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, ;/) and serratus posterior superior 

 (Fig- 71^ 0; and with the splenius (Fig. yi, b), biventer 



