After the third cut the fingers of the left hand are taken out of
the central fissure. The sections of brain as they are cut are left
lying in their order with the posterior face of the cut upward. The
same incisions are then made in the other hemisphere and the two
series of sections compared. The cerebellum, pons and medulla are
then examined as described above.
=Section of Brain in Skull.= When the skull-cap is removed by a
circular saw-cut the brain may be cut through with the saw at the
same time; or, after the skull-cap and dura have been removed, the
upper portion of the hemispheres may be sliced off by a horizontal
cut made at the level of the saw-cut. The portions removed are
examined further by sagittal cuts. The lateral ventricles are then
examined in the skull, and the remaining portion of the brain
either cut transversely _in situ_ or removed and sectioned outside
of the cranium. This method is mentioned to be condemned.
For special neuropathologic studies a number of methods have been
advised, the main purpose of which has been to preserve intact
parts of the brain having definite anatomic relationships so that
lesions may be studied by means of serial sections of the entire
system involved. The methods of =Déjerine= and =Meynert= are
employed for this purpose.
_Method of Déjerine._ After a careful examination of the cortical
surface for the presence of lesions, and of the inferior
surfaces of the crura for secondary degenerations, the pons is
cut horizontally in a plane parallel with the inferior surface
of the hemispheres and passing just above the great root of the
trifacial. The brain is thus divided into two portions, one
consisting of the two peduncles and superior portion of the
pons, the other containing the remaining portion of the pons,
the cerebellum and the medulla. The cut surfaces of the pons are
examined for evidences of degeneration in the pyramidal tracts,
and the hemispheres are separated after it has been determined
in which one the lesion is located. If the lesion is found to
be central the degenerations of importance will be found in the
tracts of the internal capsule and in the region of the tegmentum.
The hemispheres are then opened by horizontal incisions passing
through the superior third of the optic thalamus. If the lesion
is cortical the hemispheres are divided into three segments by
two transverse vertical incisions, one passing just posterior to
the splenium of the corpus callosum, the other just anterior to
the knee. The posterior segment consists of the occipital lobe
and part of the parietal; the central one contains the regions
adjacent to the fissure of Rolando, the middle portion of the
temporal convolutions, the basal ganglia, the cerebral peduncle and
corresponding portion of the pons; the anterior segment consists of
the forepart of the frontal lobe. The segments are then fixed and
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