414 THE MUSCLES AND FASCIA 



by a transverse tendinous intersection. The inner portion of this muscle is 

 usually separate and is called the biventer cervicis, from the intervention of a 

 tendon between its two fleshy bellies. 



The Fifth Layer (Fig. 313). 



Semispinalis dorsi. Extensor coccygis. 



Semispinalis colli. Intertransversales. 



Multifidus spinae. Rectus capitis posticus major. 



Rotatores spinae. Rectus capitis posticus minor. 



Supraspinales. Obliquus inferior. 



Interspinales. Obliquus superior. 



Dissection. Remove the muscles of the preceding layer by dividing and turning aside the 

 Complexus; then detach the Spinalis and Longissimus dorsi from their attachments, divide the 

 Erector spinae at its connection below to the sacral lumbar vertebrae and turn it outward. The 

 muscles filling up the interval between the spinous and transverse processes are then exposed. 



The Semispinalis dorsi (m. Semispinalis dorsi) consists of thin, narrow, 

 fleshy fasciculi interposed between tendons of considerable length. It arises 

 by a series of small tendons from the transverse processes of the lower thoracic 

 vertebrae, from the tenth or eleventh to the fifth or sixth; and is inserted, by five 

 or six tendons, into the spinous processes of the upper four thoracic and lower 

 two cervical vertebras. 



The Semispinalis colli (m. Semispinalis cervicis), thicker than the preceding, 

 arises by a series of tendinous and fleshy fibres from the transverse processes of 

 the upper five or six thoracic vertebras, and is inserted into the spinous processes 

 of four cervical vertebras, from the axis to the fifth cervical. The fasciculus 

 connected with the axis is the largest, and is chiefly muscular in structure. 



Superficial to this muscle and the preceding are the profunda cervicis artery, the princeps 

 cervicis artery, and the internal branches of the posterior divisions of the first, second, and 

 third cervical nerves; their deep surfaces lie upon the Multifidus spinae. 



The Multifidus spinae (m. multifidus') consists of a number of fleshy and ten- 

 dinous fasciculi which fill up the groove on either side of the spinous processes of 

 the vertebras, from the sacrum to the axis. In the sacral region these fasciculi 

 arise from the back of the sacrum, as low as the fourth sacral foramen, and from 

 the aponeurosis of origin of the Erector spinae; from the inner surface of the pos- 

 terior superior spine of the ilium and posterior sacro-iliac ligaments; in the lumbar 

 regions from the mammillary processes; in the thoracic region, from the transverse 

 processes; and in the cervical region, from the articular processes of the three or 

 four lower vertebras. Each fasciculus, passing obliquely upward and inward, 

 is inserted into the whole length of the spinous process of one of the vertebras 

 above. These fasciculi vary in length; the most superficial, the longest, pass from 

 one vertebra to the third or fourth above; those next in order pass from one 

 vertebra to the second or third above; while the deepest connect two contiguous 

 vertebras. 



Its superficial surface is covered by the Semispinalis dorsi, and the Semispinalis colli, and its 

 deep surface, lies upon the laminae and spinous processes of the vertebrae. 



The Rotatores spinae (mm. rotatores) are found only in the thoracic region of 

 the spine, beneath the Multifidus spinae; they are eleven in number on each side. 

 Each muscle is small and somewhat quadrilateral in form; and arises from the 



