DISSECTION OF THE BACK. 



Dissection 

 of multifi- 

 dns spin*. 



Origin of 

 multiftdus 

 spin<e 

 from pelvis, 



from lumbar, 

 dorsal, and 



cervical 

 vertebrae ; 



insertion 

 into spines. 



Relations of 

 transverso- 

 spinales ; 



and use. 



Muscles of 

 the sixth 

 layer. 



Dissection 

 of suboccipi- 

 tal muscles, 



and other 

 muscles of 

 last layer. 



Rectus 

 postitus 

 major : 



Dissection. The multifidos spinae is now to be prepared. The 

 upper part of it will be exposed by cutting through the insertion 

 of the seniispinalis, and turning aside that muscle. 



Over the sacrum the thick aponeurosis of the erector spin so 

 must be removed. In the dorsal region the multifidus spinae will 

 appear on detaching and reflecting the semispinalis from the spines. 

 The slips by which the muscle is attached to the processes of the 

 vertebrae should be defined and separated. 



The MDLTIFIDUS SPIN^ reaches from the sacrum to the axis : 

 it is larger below than above, and is smallest in the upper dorsal 

 region. It takes origin at the pelvis from the back of the sacrum 

 between the spines and the external row of processes as low as the 

 fourth aperture, from the posterior sacro-iliac ligament, from the 

 inner side of the posterior superior spine of the ilium, and from the 

 overlying tendon of the erector spinae ; in tlie loins it arises by large 

 fasciculi from the mamillary processes of the vertebrae ; in the 

 dorsal region by thinnei slips from the transverse processes ; and 

 in the neck from the articular processes of the lower four cervical 

 vertebrae. From these attachments the fibres are directed obliquely 

 upwaids and inwards, passing over from one to three vertebrae, to 

 be inserted into the spinous processes from the axis to the last lumbar 

 vertebra. 



The trans verso-spin ales are entirely concealed by the erector 

 spinae and complexus muscles ; and beneath them are the laminae 

 of the vertebrae, with the dorsal spinal plexus of veins. Internally 

 they rest against the spinous processes and the interspinal muscles. 



Action. The trans verso-spinal es of the two sides acting together 

 will extend the spine : and the muscles of one side can rotate the 

 column in the cervical and dorsal regions, turning the face in the 

 opposite direction. 



SIXTH LAYER OF MUSCLES. This layer includes a number of 

 short muscles which pass between adjacent vertebrae, or from the 

 first two vertebrae to the head. They are : 



1. The rectus capitis posticus major. 



2. The rectus capitis posticus minor. 



3. The obliquus capitis superior. 



4. The obliquus capitis inferior. 



5. The rotatores dorsi. 



6. The interspinales. 



7. The intertransversalis. 



Dissection. Between the first two cervical vertebrae and the 

 occipital bone are the recti and oblique muscles, which are to 

 be fully cleaned. 



The slips of the multifidus spinae are to be detached from the 

 spines of the vertebrae and turned downwards in order to show the 

 rotatores dorsi in the thoracic region, and the interspinal muscles in 

 the neck and loins. The intertransverse muscles of the lumbar 

 region will be exposed by removing the erector spinae. 



The RECTUS CAPITIS POSTICUS MAJOR (fig. 192, A) arises from 

 the side of the spinous process of the axis, and is inserted into the 



