THE SPINAL NERVES 



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primary divisions of the spinal nerves are quite separate from each other, and 

 are uniform in their distribution; but in the cervical, lumbar, and sacral regions 

 they form intricate plexuses previous to their distribution. The anterior primary 

 divisions of certain thoracic, lumbar, and sacral nerves give off a delicate col- 

 lection of nerve filaments to the sympathetic cord. These are called the white 

 rami communicantes or the visceral branches of the spinal nerves. 



Posterior or Dorsal Primary Divisions of the Spinal Nerves. The posterior 

 or dorsal primary divisions are here described together, inasmuch as they do not 

 enter into the formation of the important plexuses (cervical, lumbar, and sacral) 

 exclusively made up of the anterior primary divisions. 



Ventral aspect. 



FIG. 752. Distribution of cutaneous nerves. 



The Posterior or Dorsal Divisions of the Cervical Nerves (rami posterior -es). 

 The posterior division of the first cervical nerve (Fig. 753) differs from the pos- 

 terior divisions of the other cervical nerves in not dividing into an internal and 

 external branch. It is larger than the anterior division, and escapes from the 

 vertebral canal between the occipital bone and the posterior arch of the atlas 

 and beneath the vertebral artery. It enters the suboccipital triangle formed by 



