Page 274 - My FlipBook

284 ANATOMY.

white substance. It is entirely distinct and separate from the larger
sensory root from its deep origin until it passes out of the cranial cavity
through the foramen ovale, when it becomes closely united with its third
or inferior maxillary division, hereafter to be described.
The deep origin of these two roots is widely separated from their
superficial origin. Following them backward from the anterior surface
of the pons varolii, they pass directly through the pons to the medulla
oblongata, without any connection whatever with its fibres. On reach-
ing the medulla they form three main divisions, one anterior and two
posterior.
The Anterior or 3Iotor Division arises from the motor nucleus of
the fifth nerve, which is composed of large, ramified, and pigmented
cells situated below the lateral angle of the fourth ventricle, anterior to
the inferior facial nucleus, and on the proximal side of the large sensory
nucleus of the fifth nerve. It also arises from the gray matter at the
anterior portion of the iter beneath the corpora quadrigemina. As it
passes toward the pons it receives fibres which arise from the raphe.
The fibres have their origin in the nucleus of the opposite side or in
the pyramidal tract.
The Two Posterior or Sensory Divis^ions give general sensibility to the
face and head, extending as far back as its vertex. These divisions are
the superior and inferior.
The Superior or Larger Division arises from the superior sensory
nucleus of the fifth nerve. This nucleus is situated at the side of the
motor nucleus, and is composed of nerve-cells which are less compactly
arranged, but in greater numbers than the motor nucleus.
The Inferior or Smaller Diinsion . is a well-defined bundle of nerve-
fibres which arises from the inferior nucleus of the fifth nerve. This
is composed of cells situated in the gelatinous substance which consti-
tutes the tubercle of Rolando.
From their sujierficial origin these two roots extend obliquely upward
and forward across the summit of the petrous portion of the .temporal
bone, and jwiss through an oval opening in the dura mater into the mid-
dle fossa of the brain-case. The larger posterior sensory root terminates
in the ganglion of Gasser,' which is situated in a depression on the supe-
rior part of the anterior surface near the apex of the petrous portion
of the temporal bone. This ganglion is broad, flattened, and somewhat
semilunar or crescent-shaped, and from this fiict is often called the semi-
lunar ganglion of the fifth nerve. Its convexity is directed forward and
slightly upward. The cells of this ganglion are unipolar in shape. Its
surfaces are striated, and it receives on its inner side filaments of com-
munication from the carotid ])lexus of the sympathetic nervous system."
' The structure of tliis gantjlion was first recognized by Gasser, professor of anatomy
in Vienna. His observations, however, were published by Hirsch, a pupil of Gasser,
in 1765 (Hirsch, Paria Qiiiiiti Nervonum encephali, Viennoe, 1765), in Ludwig (Scrip-
tores Nervoinyiri minnres selccli, Lipsife, 1791, tonius i. pp. 244 et seq.). Hirsch first gave
it the name of (rasserian ganglion.
Some authors call it ( 'asserian ganglion, probably confounding Gasser with Casserius.
Casserius in his anatomical figures describes many parts of the brain and nerves, but
says nothing of the ganglion of the fifth (Casserius. Anatnmische Tofdn, Franckfurt-am-
Mayn, 1756). (Flint's Physloloyy of the Nervous iiystem,Yo\. i. p. 185.)