DISSECTION OF THE HEAD AND NECK 237 



(c) Posterior rami of lumbar nerves (rami posteriores Nn. lum- 



balium ) . 



(ca) Medial rami (rami mediates) . 



(cb) Lateral rami (rami later ales). 



(d) Posterior rami of sacral and coccygeal nerves (rami posteriores 



Nn. sacralium et coccygei). 



Opening the Vertebral Canal. 



Carefully remove all muscles and tendons from the spinous 

 processes and arches of the vertebrae from the occipital bone to 

 the tip of the coccyx, avoiding injury, however, to the posterior 

 rami of the spinal nerves (rami posteriores Nn. spinalium). 

 Place high blocks under the thorax and let the head hang over 

 the end of the table. 



The vertebral canal (canalis vertebralis) may be opened from 

 behind in any one of four different ways: (a) with the double 

 rhachiotome, (b) with a saw, (c) with mallet and chisel, (d) 

 with bone-forceps. 



(a) With the Double Rhachiotome. Place the saws of Luer's double 

 rhachiotome on the cervical portion of the vertebral column; seize the 

 handle with the right hand, pressing down from above upon the rhachi- 

 otome with the left hand; saw (in the direction in which the teeth are set) 

 with quick, rapidly repeated strokes through the vertebral arches. As 

 soon as the saw has gone through, the same process is repeated a little 

 lower down, and so on until the whole posterior wall of the vertebral 

 column has been cut through as far as the last lumbar vertebra. Between 

 the last lumbar vertebra and the sacrum cut through the ligamenta flava; 

 introduce the vertebral forceps below the posterior arch of the last lumbar 

 vertebra, seize hold of it and, grasping the forceps with both hands, tear 

 away in one piece the whole posterior wall of the vertebral canal from 

 the lumbar region to the occipital bone. If the cervical portion be not 

 quite sawn through, apply the rhachiotome again and cut in a reverse 

 direction. 



( b ) With a Saw. One may use a simple saw, cutting through first one 

 side and then the other. The saw should pass close behind the articular 

 processes and should be directed slightly obliquely, so that the cut passes 

 a little medialward in the depth. It may be necessary to use the hammer 

 and chisel also. Neelsen recommends the use of the " fox-tail saw." 



(c) With Mallet and Chisel The vertebral arches may be chiselled 

 instead of sawn through, if desired, but the tyro is apt to injure the cord. 

 Special chisels (one for each side) are manufactured for the purpose, but 

 a good heavy plain chisel works well. 



(d) With Bone-forceps. Cut through the root of each vertebral arch 

 (radix arcus vertebrae} (0. T. pedicle) on each side, just ventral to the 

 superior articular processes, and thus remove the whole posterior wall of 

 the vertebral canal. This method has the advantage that it opens up all 

 intervertebral foramina and permits of the removal of the spinal ganglia 

 and the proximal portion of each spinal nerve along with the spinal cord. 



