Muscles of the Back. 



293 



338. Short muscles of the back (P^ layer), viewed from behind. 



(The 111. seiiiispiiiahs eiipitis has been removed mi the left side.) 



Protubcraiitia 



occipitalis 



externa 



Processus 

 mastoideus 



M. semispiualis capitis 



semispinalis cervicis 



Processus spinosus verte 

 brae cervicalis VII 



Costa I - 



( 



Processus 



spinosus 



vertebrae 



thorac. VI 



M. semi- 

 spinalis 

 dorsi 



M. spinalis (0. T. inner divi- 

 sion of erector spinae) (see Y'vj^. 

 336), very thin, lornis the metlial 

 part of the m. sacrospinalis and ex- 

 tends between spinous processes. 

 M. spinalis dorsi. Orif,'in: 

 tendinous from the two upper- 

 most lumbar and the two (or 

 three) lowermost thoracic verte- 

 brae, intimately fused with the 

 m. longissimus. Insertion: 

 tendinous to the thoracic ver- 

 tebrae from the %^^ (or 8th) to 

 the 2"i inclusive; one vertebra 

 (10^*1 or y'b) is' passed over 

 without attachment. 



M. spinalis cervicis (0. T. 

 s])inalis colli), very variable. 

 Origin: two uppermost tho- 

 racic and two lowermost cervical 

 vertebrae. Insertion: A^^ to 

 2"d cervical vertebra. 



Action: they extend the spi- 

 nal column. Innervation : rami 

 mediales of the rami posteriores 

 of the nn. cervicales III VIII 

 and thoracales I XII. 



M. spinalis capitis see under 

 m. semispinalis capitis. 



M. semispinalis (see also Fig-. 

 ^37) is the superficial and most 

 vertical layer of the fiber masses. 

 which, running obliquely upward 

 from the procc. transversi to the 

 procc. spinosi, fills up the groove 

 between the jirocc. spinosi and 

 transversi as a triangular prisma- 

 tic cord ; the fibers pass over more 

 than four vertebral bodies before 

 becoming attached. The muscle 

 is absent in the lumbar region. 



M. semispinalis dorsi. Origin: procc. transversi of the six lower thoracic vertebrae. 

 Insertion: j)rocc. spinosi of the six upper thoracic and two lower cervical vertebrae. 



M. semispinalis cervicis (0. T. semispinalis colli). Origin: procc. transversi of the 

 six upper thoracic vertebrae. Insertion: procc. spinosi of the 5tii 2nd cervical vertebra. 



Action: they bend the spinal column backward and rotate it toward the opposite side. 



M. semispinalis capitis (0. T. complexus) (see also Figs. 296 and 335). Form: flat, 

 oblong-quadrangular, thick. Position: bounded medianward by the lig. nuchae, lateral- 

 ward by the m. longissimus capitis, covered in large part by the mm. splenii and trapezius. 

 Origin: procc. transversi of tlie six upper thoracic vertebrae, procc. transversi et articulares 

 of the 3 4 lower cervical vertelirae and procc. spinosi of the uppermost thoracic and lowermost 

 cervical vertebrae. The fibers coming from the procc. spinosi are sometimes separated so as 

 to form an independent muscle, the m. spinalis capitis. Insertion: the fibers run parallel 

 upward and snmewhat medianward to the under surface of the si[uama occipitalis; they are 

 interrupted, especially medianward, by one or several jagged intermediate tendons. Action: 

 it draws the head backward and raises the face toward the other side. 



Innervation: rami mediales of the rami posteriores of the nn. cervicales II YIII 

 and thoracales I XII. 



k 



Proc. spin. 



vertebrae 



thoracalis 



XII 



Costa Xn 



^V- 



