spect do the posterior roots differ from the anterior? 760.
When do the two roots unite, and where do they pass?

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761. The _spinal nerves_ are divided into--

Cervical, 8 pairs,
Dorsal, 12 "
Lumbar, 5 "
Sacral, 6 "

762. The four lower cervical and upper dorsal pass into each other and
then separate to reunite. This is called the _brach'i-al plex'us_.
From this plexus six nerves proceed, which ramify upon the muscles and
skin of the upper extremities.

763. The last dorsal and the five lumbar nerves form a plexus called
the lumbar, similar to that of the cervical. Six nerves pass from this
plexus, which ramify upon the muscles and skin of the lower
extremities.

764. The last lumbar and the four upper sacral unite to form the
sacral plexus. From this plexus five nerves proceed, that are
distributed to the muscles and skin of the hip and lower extremities.

765. The SYMPATHETIC NERVE[19] consists of a series of _Gan'gli-a_, or
knots, extending each side of the spinal column, forming a chain its
whole length. It communicates with both the cranial and spinal nerves.
With the exception of the neck, there is a ganglion for each
intervertebral space. These ganglia are composed of a mixture of
cineritious and medullary matter, and are supposed to be productive of
peculiar nervous power.

[19] The structure of this nerve is very complicated, and different
physiologists ascribe to it various functions. The character of
its diseases are not well understood.

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761. Give the division of the spinal nerves. 762. What nerves
constitute the brachial plexus? How many nerves pass from this plexus?
763. How many nerves from the lumbar plexus, and where do they ramify?
764. How is the sacral plexus formed? 765. Of what does the
sympathetic nerve consist? How is the sympathetic nerve distributed?
What exception? Of what are the ganglia composed?

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[Illustration: Fig. 131. A beautiful representation of the sympathetic
ganglia and their connection with other nerves. It is from the grand
engraving of Manec, reduced in size. A, A, A, The semilunar ganglion and
solar plexus, situated below the diaphragm and behind the stomach. This
ganglion is situated in the region (pit of the stomach) where a blow
gives severe suffering. D, D, D, The thoracic ganglia, ten or eleven in
number. E, E, The external and intern