88 HEAD AND NECK 



The origins of the eight cervical nerves lie between the 

 level of the atlas and the level of the spine of the sixth 

 cervical vertebra ; the origins of the first six thoracic nerves 

 extend from the sixth cervical to the third thoracic spine ; 

 the origins of the lower six thoracic nerves lie between the 

 third and the ninth thoracic spines ; and the origins of the 

 lumbar and sacral nerves are between the ninth thoracic and 

 the first lumbar spine. 



Mode of Exit of Spinal Nerves from Vertebral Canal. 

 The lower six cervical nerves, the thoracic nerves, and the 

 lumbar nerves make their exit through the intervertebral 

 foramina; whilst each of the two rami of the upper four 

 sacral nerves finds its way out by a sacral foramen. The 

 upper two cervical nerves, the fifth sacral nerve, and the 

 coccygeal nerve, however, follow a different course. The 

 sub-occipital emerges by passing over the posterior arch of 

 the atlas, and the second cervical nerve by passing over the 

 vertebral arch of the epistropheus (O.T. axis). The fifth 

 sacral and the coccygeal nerve leave the sacral canal through 

 its lower aperture (Fig. 25). 



Dissection. The nerve-roots of one or two spinal nerves in 

 each region should be followed into the corresponding inter- 

 vertebral foramina. That can be easily done by snipping away 

 the articular processes with the bone-forceps. The position of 

 the ganglion on the posterior root, the connections of the sheath 

 of dura mater, the union of the two roots to form the spinal nerve- 

 trunk, and the division of the trunk into the anterior and posterior 

 rami can then be studied. An attempt should also be made, at 

 the same time, to discover the minute ramus meningeus. It 

 is a fine twig which is formed by the union of a small filament 

 from the spinal nerve-trunk with a minute branch from the 

 sympathetic trunk. It takes a recurrent course through the 

 intervertebral foramen to end in the bones and periosteum and 

 meninges of the vertebral canal. 



Ganglia Spinalia. The spinal ganglia are oval swellings 

 developed upon the posterior nerve-roots, just before they 

 unite with the anterior roots to form the spinal nerve-trunks. 

 They are found upon the posterior roots of all the nerves, 

 except, occasionally, those of the sub-occipital and the coccy- 

 geal nerves. 



The ganglia are formed upon the posterior nerve -roots 

 as they lie in the intervertebral foramina, except in the 

 cases of the first two cervical and the sacral and coccygeal 

 nerves. The ganglia of the first two cervical nerves lie upon 



