THE SPINAL NERVES 



917 



The Spinal Ganglia (ganglion spinale) are collections of nerve cells on the posterior 

 roots of the spinal nerves. Each ganglion is oval in shape, reddish in color, and 

 its size bears a proportion to that of the nerve root on which it is situated; it is 

 bifid medially where it is joined by the two bundles of the posterior nerve root. 

 The ganglia are usually placed in the intervertebral foramina, immediately outside 

 the points where the nerve roots perforate the dura mater, but there are exceptions 

 to this rule; thus the ganglia of the first and second cervical nerves lie on the verte- 

 bral arches of the atlas and axis respectively, those of the sacral nerves are inside 

 the vertebral canal, while that on the posterior root of the coccygeal nerve is placed 

 within the sheath of dura mater. 



Structure (Fig. 638). The ganglia consist chiefly of unipolar nerve cells, and from these the 

 fibers of the posterior root take origin the single process of each cell dividing after a short course 

 into a central fiber which enters the medulla spinalis and a peripheral fiber which runs into the 

 spinal nerve. Two other forms of cells are, however, present, viz. : (a) the cells of Dogiel, whose 

 axons ramify close to the cell (type II, of Golgi), and are distributed entirely within the ganglion; 

 and (i>) multipolar cells similar to those found in the sympathetic ganglia. 



The ganglia of the first cervical nerve may be absent, while small aberrant ganglia consisting 

 of groups of nerve cells are sometimes found on the posterior roots between the spinal ganglia 

 and the medulla spinalis. 



Each nerve root receives a covering from the pia mater, and is loosely invested 

 by the arachnoid, the latter being prolonged as far as the points where the roots 

 pierce the dura mater. The two roots 

 pierce the dura mater separately, each 

 receiving a sheath from this membrane; 

 where the roots join to form the spinal 

 nerve this sheath is continuous with the 

 epineurium of the nerve. 



Size and Direction. The roots of the 

 upper four cervical nerves are small, 

 those of the lower four are large. The 

 posterior roots of the cervical nerves 

 bear a proportion to the anterior of 

 three to one, which is greater than in 

 the other regions; their individual fila- 

 ments are also larger than those of the 

 anterior roots. The posterior root of 

 the first cervical is an exception to this 

 rule, being smaller than the anterior 

 root; in eight per cent, of cases it is 

 wanting. The roots of the first and 

 second cervical nerves are short, and 

 run nearly horizontally to their points 

 of exit from the vertebral canal. From 



e second to the eighth cervical they 

 are directed obliquely downward, the 

 obliquity and length of the roots succes- 

 sively increasing; the distance, however, 

 between the level of attachment of any 

 of these roots to the medulla spinalis and 

 the points of exit of the corresponding 

 nerves never exceeds the depth of one 

 vertebra. 



The roots of the thoracic nerves, with the exception of the first, are of small 

 size, and the posterior only slightly exceed the anterior in thickness. They increase 

 successively in length, from above downward, and in the lower part of the thoracic 



POSTERIOR 

 NERVE 

 ROOTS 



POSTERIOR 

 ROOTS - 



POSTERIOR 

 ROOTS 



ANTERIOR 

 NERVE 

 ROOTS 



LIGAMENTUM 

 DENTICULATUM 



DURA 

 'OPENED 



ANTERIOR 

 ROOTS 



SPINAL NERVE 

 IN ITS RIAL 

 SHEATH 



ANTERIOR 

 ROOTS 



POSTERIOR 

 ROOTS 



LIGAMENTUM 

 DENTICULATUM 

 ANTERIOR 

 ROOTS 



SPINAL NERVE 

 IN ITS SHEATH 



FIG. 790. A port 

 right lateral surface, 

 show the nerve roots. 



ion of the spinal cord, showing its 

 The dura is opened and arranged to 

 (Testut.) 



