226 CLINICAL APPLIED ANATOMY. 



for some reason remaining unusually large, and embryonic 

 tissue persisting around it. In some cases a central canal may 

 be recognised, distinct from the cavities in the nerve tissue. 

 To explain the separation of the two it is assumed that the 

 posterior portion of the primitive canal becomes shut off from 

 the anterior part, and persists in the form of a cavity in the 

 region of the posterior septum of the cord. In other instances 

 cavities lie in the posterior horns of the grey matter, and may 

 be due to the disintegration of the embryonic tissue which forms 

 the basis of these. 



Syringomyelia usually occurs in the cervico-dorsal region, and 

 the disease accordingly manifests itself chiefly in the arms. The 

 symptoms are referable to disease of the grey matter, and consist 

 of local muscular atrophy with dissociation of sensation. The 

 sense of touch is usually retained whilst painful and thermal 

 sensations may be absent. Trophic lesions are also met with. 



TABLE OF LEVELS OP OEIGIN AND EXIT OF SPINAL NERVES. 



Roots. Level of Origin from Cord. Point of Exit from Canal. 



C.I ... Just above arch of atlas Between atlas and occiput. 



2 ... Kanges from just above to just below 



posterior tubercle of atlas Above axis. 



3 ... At or just above spine of axis Above 3rd cervical vert. 



4 ... Kanges from spine of axis to spine of 3rd 



cervical vertebra ... Above 4th cervical vert. 



5 ... Kanges from lower border of spine of axis 



to lower border of spine of 4th cervical v. Above 5th cervical vert. 



6 ... Ranges between lower borders of spines of 



3rd and 5th cervical vertebra Above 6th cervical vert. 



7 ... Eanges between top of 4th and bottom of 



6th cervical spines Above 7th cervical vert. 



8 ... Ranges between upper borders of 5th to 7th 



cervical spines ... ... ... ... Above 1st dorsal vert. 



D. 1 ... Ranges between space above 6th and space 



below 7th spines ... ... ... ... Above 2nd dorsal vert. 



2 ... Ranges between lower borders of 6th cervical 



and 1st dorsal spines Above 3rd dorsal vert. 



3 ... Ranges between upper edge of 7th cervical 



to lower border of 2nd dorsal spine . . . Above 4th dorsal vert. 



4 ... Ranges from top of 1st to top of 3rd dorsal 



spine ... ... ... Above 5th dorsal vert. 



5 ... Ranges from top of 2nd to top of 4th dorsal 



spine ... ... Above 6th dorsal vert. 



6 ... Ranges from lower edge of 2nd dorsal 



spine to upper of 5th Above 7th dorsal vert. 



7 ... Ranges from top of 4th to bottom of 5th 



dorsal spine ... ... Above 8th dorsal vert. 



