1. Sectio praefrontalis, through the frontal lobe about 5 cm. in front of and parallel to the central fissure, exposing the cortex and medulla of the three frontal convolutions, gyrus orbitalis, and the convolutions of the median surface of the frontal lobe.
2. Sectio pediculo-frontalis, through the “foot” of the frontal convolutions, exposing the three frontal convolutions, anterior end of the island of Reil, gyrus orbitalis, corpus callosum, head of caudate nucleus, anterior portion of lentiform nucleus and lenticular striated portion of the internal capsule.
3. Sectio frontalis, through the anterior central convolution, showing the anterior central convolution, island of Reil, the temporal convolutions, corpus callosum, tail of caudate nucleus, the optic thalamus, middle portion of lentiform nucleus, the anterior portion of the lenticular part of the internal capsule, the external capsule and claustrum.
4. Sectio parietalis, through the posterior central convolution, showing the same, the island of Reil, temporal convolutions, corpus callosum, tail of caudate nucleus, posterior end of optic thalamus and lentiform nucleus, posterior end of the lenticular-optic part of internal capsule, the external capsule and the claustrum.
5. Sectio pediculo-parietalis, through the foot of the parietal convolution, 3 cm. posterior to the fissure of Rolando, showing superior and inferior parietal lobules, temporal convolutions, corpus callosum, extreme posterior portion of optic thalamus and tail of caudate nucleus.
6. Sectio occipitalis, about 1 cm. in front of the parieto-occipital sulcus, showing cortex and medulla of occipital lobe.
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 hardened and cut on a brain-microtome. The anterior and posterior segments are sectioned vertically transversely, the central segment is cut horizontally. By this method cortical lesions may be accurately located, and the entire course of degenerating fibres followed out.