278 MUSCLES AND FASCIA. 



Nerves. The Erector spinse and its subdivisions in the dorsal region are sup- 

 plied by the external posterior branches of the lumbar and dorsal nerves ; the 

 Cervicalis ascendens, Transversalis colli, Trachelo-mastoid, and Spinalis cervicis, 

 by the external posterior branches of the cervical nerves ; the Complexus, by the 

 internal posterior branches of the cervical nerves, the suboccipital and great 

 occipital. 



FIFTH LAYER. 



Semi-spinalis Dorsi. Extensor Coccygis. 



Semi-spinalis Colli. Inter-transversales. 



Multifidus Spinae. Bectus Capitis Posticus Major. 



Rotatores Spinae. Rectus Capitis Posticus Minor. 



Supra-spinales. Obliquus Superior. 



Inter-spinales. Obliquus Inferior. 



Dissection. The muscles of the preceding layer must be removed by dividing and turning 

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

 and divide the Erector spinae at its connection below to the sacral and lumbar spines, and turn 

 it outward. The muscles filling up the interval between the spinous and transverse processes 

 are then exposed. 



The Semi-spinales muscles connect the transverse and articular processes to the 

 spinous processes of the vertebra?, extending from the lower part of the dorsal 

 region to the upper part of the cervical. 



The semi-spinalis dorsi consists of a thin, narrow, fleshy fasciculus, interposed 

 between tendons of considerable length. It arises by a series of small tendons 

 from the transverse processes of the lower dorsal 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 dorsal and lower two cervical vertebrae. 



The semi-spinalis colli, thicker than the preceding, arises by a series of tendinous 

 and fleshy points from the transverse processes of the upper four dorsal vertebrae, 

 and from the articular processes of the cervical vertebrae (lower four) ; and is 

 inserted into the spinous processes of four cervical vertebrae, from the axis to the 

 fifth cervical. The fasciculus connected with the axis is the largest, and chiefly 

 muscular in structure. 



Relations. By their superficial surface, from below upwards, with the Longis- 

 simus dorsi, Spinalis dorsi, Splenius, Complexus, the profunda cervicis and prin- 

 ceps cervicis arteries, and the posterior cervical plexus of nerves. By their deep 

 surface, with the Multifidus spinae. 



The Multifidus Spinse consists of a number of fleshy and tendinous fasciculi, 

 which fill up the groove on either side of the spinous processes of the vertebrae, 

 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. In the iliac region, they arise from the inner 

 surface of the posterior superior spine, and posterior sacro-iliac ligaments. In 

 the lumbar and cervical regions, they arise from the articular processes ; and in 

 the dorsal region, from the transverse processes. Each fasciculus, ascending 

 obliquely upwards and inwards, is inserted into the lamina and whole length of 

 the spinous process of the vertebra 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 ; whilst 

 the deepest connect two contiguous vertebrae. 



Relations. By its superficial surface, with the Longissimus dorsi, Spinalis dorsi, 

 Semi-spinalis dorsi, and Semi-spinalis colli. By its deep surface, with the laminae 

 and spinous processes of the vertebrae, and with the Eotatores spinae in the dorsal 

 region. 



The Rotatores Spinse are found only in the dorsal region of the spine, beneath 

 the Multifidus spinae ; they are eleven in number on each side. Each muscle, 



