OF THE BACK. 437 



spinous processes of the fifth, sixth, and seventh cervical vertebrae, and occasionally 

 from the first and second dorsal, and is inserted into the spinous process of the 

 axis, and occasionally into the spinous processes of the two vertebrae below it. 

 This muscle was found absent in five cases out of twenty-four. 



The Complexus is a broad thick muscle, situated at the upper and back part of 

 the neck, beneath the Splenius, and internal to the Transversalis colli and Trachelo- 

 mastoid. It arises, by a series of tendons, about seven in number, from the tips 

 of the transverse processes of the upper three dorsal and seventh cervical vertebrae, 

 and from the articular processes of the three cervical above this. The tendons, 

 uniting, form a broad muscle, which passes obliquely upward and inward, and 

 is inserted into the innermost depression between the two curved lines of the 

 occipital bone. This muscle, about its middle, is traversed by a transverse tendi- 

 nous intersection. 



The Biventer cervicis is a small fasciculus, situated on the inner side of the 

 preceding, and in the majority of cases blended with it ; it has received its name 

 from having a tendon intervening between two fleshy bellies. It is sometimes 

 described as a separate muscle, arising, by from two to four tendinous slips, from 

 the transverse processes of as many of the upper dorsal vertebrae, and inserted, 

 on the inner side of the Complexus, into the superior curved line of the occipital 

 bone. 



Relations. The Complexus is covered by the Splenius and the Trapezius. It 

 lies on the Rectus capitis posticus major and minor, the Obliquus capitis superior 

 and inferior, and on the Semispinalis colli, from which it is separated by the pro- 

 funda cervicis artery, the princeps cervicis artery, and branches of the posterior 

 cervical plexus of nerves. The Biventer cervicis is separated from its fellow of 

 the opposite side by the ligamentum nuchae. 



Nerves. The Erector spinae and its subdivisions in the dorsal region are 

 supplied by the external branches of the posterior divisions of the lumbar and 

 dorsal nerves, while its subdivisions in the cervical region, the Transversalis colli 

 and Trachelo-mastoid, are supplied by the external branches of the posterior 

 divisions of the cervical nerves ; the Complexus, by the internal branches of the 

 posterior divisions of the cervical nerves, the suboccipital and great occipital. 

 The Spinalis colli is supplied by the internal branches of the posterior divisions 

 of the cervical nerves ; and the Spinalis dorsi, by the internal branches of the pos- 

 terior divisions of the dorsal nerves. 



Fifth Layer. 



Semispinalis dorsi. Extensor coccygis. 



Semispinalis colli. Intertransversales. 



Multifidus spinae. Rectus capitis posticus major. 



Rotatores spinae. Rectus capitis posticus minor. 



Supraspinales. Obliquus capitis superior. 



Interspinales. Obliquus capitis inferior. 



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 and lumbar spines, and turn it outward. 

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



The Semispinalis dorsi (Fig. 288) 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 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 Semispinalis colli, thicker than the preceding, arises by a series of tendinous 

 and fleshy fibres from the transverse processes of the upper four dorsal vertebrae 

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

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



