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THE NERVOUS 8YSTEM. 



FIG. 415.- Superficial and deep distribution of the posterior divisions of the spinal nerves (after Hirsehfeld 

 and Leveill6). On the left side the cutaneous branches are represented lying on the superficial layer of mus- 

 cles. On the right side the superficial muscles have been removed, the Splenius capitis and Complexus divided 

 in the neck, and the Erector spinse divided and partly removed in the back, so as to expose the posterior divis- 

 ions of the spinal nerves near their origin, a a. Lesser occipital nerve from the cervical plexus. 1. External 

 muscular branches of the first cervical nerve, and union by a loop with the second. 2, placed on the Rectus 

 capitis posticus major muscle, marks the great occipital nerve, passing round the short muscles and piercing 

 the Complexus : the external branch is seen to the outside. 3. External branch from the posterior division of 

 the third nerve. 3'. Its internal branch, sometimes called the third occipital. 4' to 8'. The internal branches 

 of the several corresponding nerves on the left side. The external branches of these nerves, proceeding to 

 muscles, are displayed on the right side, A 1 to d 6, and thence to d 12. External muscular branches of the pos- 

 terior divisions of the twelve dorsal nerves on the right side, d 1' to d 6'. The internal cutaneous branches of 

 the six upper dorsal nerves on the left side, d 7' to d 12'. Cutaneous twigs from the external branches of the 

 six lower dorsal nerves. 1 1. External branches from the posterior divisions of several lumbar nerves on the 

 right side, piercing the muscles, the lower descending over the gluteal region. I' I'. The same, more super- 

 ficially, on the left side, s s. The issue and union by loops of the posterior divisions of four sacral nerves on the 

 right side, s' s'. Some of those distributed to the skin on the left side. 



The Upper Dorsal Nerves. The anterior divisions of the second, third, fourth, 

 fifth, and sixth dorsal nerves and the small branch from the first dorsal are 



