292 



Muscles of the Back. 



I'rotaberantiii 



occipitalis 



externa 



M. loDgissimus 

 capitis 



M. loiigissimtis 

 cervicis 



337. Long muscles of the back (2"^MaYer), viewed from behind. 



(The mm. ihocostiiles have been removed; the mm. longissimi dorsi have been reflected outward ; 



thi> m. long'issimus cervicis has been, on the right side, drawn hiteralward, on the left side, 



medianward; the m. longissimiis ca]iitis has been drawn medianward on the right side.) 



M. lougissimus (0. T. middle division 

 of erector spinae) (see also Fig. 336) is the 

 middle bundle of the m. sacrospinalis ; it 

 extends (in the back only by its medial 

 digitations) between the transverse pro- 

 cesses or their homologues. 



M. lougissimus dorsi. Ori- 

 gin: it receives medianward 

 several short, accessory bundles 

 from the transverse processes of 

 the 12th 7th thoracic vertebra. 

 Insertion: l^t, by thin, la- 

 teral processes, fleshy below, 

 tendinous above, to the transverse 

 jirocesses of the 5th jst Imnbar 

 vertebra and the angles of the 

 12th 2nd i-ib (see Fig. 336); 

 2"<J^ by medial processes, below 

 fleshy, above tendinous, to the 

 procc. accessorii of the 5th to 

 1st lumbar vertebrae and the 

 procc. transversi of all the tho- 

 racic vertebrae. Action: it 

 bends the spinal column back- 

 ward and toward the same side. 

 M. longissiniHS cervicis (see 

 also Fig. 335). Form: flat, thin. 

 Position: medianward from the 

 m. iliocostahs cervicis, lateral- 

 ward from the m. longissimus 

 capitis. Origin: uppermost 4 6 

 thoracic vertebrae. Insertion: 

 the middle cervical vertebrae. 

 Action: it bends the neck 

 Itackward and to\\ard the same 

 side. 



M. loiig'issimus capitis (0. 

 T. tracbelomastoid) (see also Fig. 

 335). Form: flat, oblong-(iua- 

 drangular, thin: usually fused 

 with the preceding muscle. Posi- 

 tion: medianward from the m. 

 longissimus cervicis, lateralward 

 from the m. semispinalis capitis. 

 Origin: procc. transversi of the 

 3rd_list thoracic vertebra and 

 procc. articulares of the 7th 3rd 

 cervical vertebra. Insertion: 

 thickened and tendinous to the 

 proc. mastoideus. Action: it 

 draws the head backward and 

 toward the same side. 



Innervation: rami laterales 

 of the rami posteriores of the 

 nn. cervicales II VIII, thora- 

 cales I XII, lumbales I V, and 

 sacrales I and IT. 



Mm. 



intercostale 



externi 



M. 

 semi- 

 spinalis 

 dorsi 



