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SIR CHARLES BELL'S DIVISION OF NERVES.

membrane; and, according to Reil,' of an external envelope, called

neurilemma, which, in the opinion of most anatomists, is nothing more than an areolar envelope, similar to that which surrounds the vessels and muscular fibres.

Until of late years, the nerves were universally divided, according to their origin, into encephalic and spinal; but, more recently, anatomical divisions have been proposed,

based upon the uses they appear to fulfil in the economy. For one of the most beautiful of this kind we are mainly indebted to Sir Charles Bell. It has been already seen, that the encephalic nerves are connected with the encephalon by one root, whilst the spinal nerves arise from two; the one connected with the anterior tract of the spinal marrow, the other with the posterior. If these different roots be ex

A portion of the Spinal Marrow, show-
ing the Origin of some of the Spinal
Nerves.

1. Anterior or motor root of a spinal

nerve.

2. Posterior or sensory root.

3. Ganglion connected with the latter.

Plans in outline, showing the Front A, and
the Sides B, of the Spinal Cord, with the
Fissures upon it; also sections of the
Gray and White Matter, and the Roots
of the Spinal Nerves.

a, a. Anterior. p, p. Posterior fissure. b.
Posterior, and c. Anterior horn of gray mat-
ter. e. Gray commissure. a, e, c. Anterior
white column. c, e, b. Lateral columns.
a, e, b. Antero-lateral column. b, e, p. Pos-
terior columns. r. Anterior, and s. Poste-
rior roots of a spinal nerve.

perimented on, we meet with results varying considerably. If we divide the anterior root, the part to which the nerve is distributed is deprived of motion; if the posterior root be cut, the part is deprived of sensibility. We conclude, therefore, that each of the spinal nerves consists

'De Structurâ Nervorum, Hal. 1796.