and chisel is allowable; the calvarium must be freed entirely by sawing. The calvarium should be examined at the time of removal.

The next step is to inspect the dura. Under normal conditions it is not tense in the frontal region, but can be picked up with the forceps or fingers. If the dura is not thickened, the convolutions normally should be visible through it. The longitudinal sinus is opened with knife or scissors and its contents examined. Pacchionian granulations are not infrequently found projecting into it.

To remove the dura, cut through it with scissors or knife along the same lines in which the calvarium was sawn. Turn back each half of the dura and examine the surface of the convolutions and the inner surface of the dura. The convolutions should be distinct and rounded, not flattened, with obliteration of the gyri, as occurs when there is internal pressure.

The Pacchionian granulations are situated along the longitudinal fissure and may grow through the dura and form depressions in the calvarium. There may be apparent adhesions between the dura and pia due to veins passing from one to the other. The dura is still further freed by seizing the two halves anteriorly and lifting them up until the falx is tense at its insertion into the crista galli. Pass a knife in parallel to the falx, on the left side, with the edge forward, as far as the cribriform plate; turn it to the right and cut until the falx yields. Withdraw the knife in the same manner in which it was inserted. Next draw the dura back. It is usually more or less attached along the longitudinal fissure by Pacchionian granulations and by blood-vessels. These may be cut or torn through. Do not cut the dura posteriorly, but let it hang down.

To remove the brain, insert the two fore fingers, or the first and second fingers of the left hand, anteriorly between the dura and the frontal lobes, one on each side of the falx cerebri, and draw the brain gently back until the optic nerves are visible. Ordinarily, the olfactory nerves come away from the cribriform plate without trouble, but sometimes have to

be freed with the point of the knife. With a long, slenderbladed knife divide the optic nerves as far forward as possible while holding the brain back with the left hand. Continue to draw the brain carefully back and divide the cranial nerves

and the carotids. Then draw forward first the left, then the right temporal lobe, and cut the tentorium close to its attachment to the petrous portion of the temporal bone with a sawing motion, using the tip of the knife. Insert the knife at the side close to the squamous bone, and cut from there

in toward the foramen magnum. Then cut the nerves given off from the medulla oblongata while supporting the convexity of the brain in the left hand.

Lastly, carry the knife as far as possible into the spinal canal, and divide the cervical cord by an oblique incision from each side, severing the vertebral arteries with the same stroke. Better than a knife is the myelotome, because it gives a cross-section of the cord and allows more of it to be removed.

The brain is now to be removed by passing the first and second fingers of the right hand in on either side of the cord, and everting the brain while still supporting it posteriorly with the left hand.

Before proceeding to open the brain it is best to examine the base of the skull, particularly the dura, of which the sinuses should be incised, and the hypophysis cerebri.

If there is a suspicion of a fracture at the base, strip off the dura, so as to give a better opportunity for examination of the bone.

The brain should be weighed before it is dissected. The average weight in an adult male is 1358 grams; in an adult woman, 1235 grams.

External Examination of the Brain.-Place the brain with the base uppermost and with the cerebellum toward the operator. Examine first the pia and the cranial nerves, then the arteries, especially the middle cerebral and its branches on each side in the fissure of Sylvius, for it is here that emboli most frequently lodge. The pia bridging the fissure of Sylvius can sometimes be torn through, but usually has to be cut.

It is important, particularly in cases of obscure cerebral symptoms, to feel gently with the finger-tips all over the surface of the brain for any areas of increased density, because patches of sclerosis may in that way be found which might otherwise be overlooked.

By stripping off the pia-a procedure not often advisable -adhesions over pathological areas can sometimes be found pointing to the lesions beneath, but the pia should not be

stripped from those portions which are to be examined microscopically. To remove the pia an incision is made on the median surface of each hemisphere just above the corpus callosum from one extremity to the other, and the pia stripped back first from the median and then from the convex surface. The stripping is done by means of the fingers, with occasional aid from the forceps.

Section of the Brain.-There are several methods of cutting up the brain, no one of which is particularly suitable to all occasions. That method must be chosen which is most fitted to the individual case and to the use to which the tissue is to be put.

The ideal method from a neuro-pathological standpoint would undoubtedly be to harden the brain entire, and then to make serial frontal sections thin enough for microscopical purposes through the whole organ. The nearest approach to this ideal method is to harden the brain entire in formaldehyde, a process occupying ten days to two weeks (see page 325), to make thin serial sections, to mordant the sections, divided if necessary into smaller pieces, in a chrome salt (preferably by Weigert's quick method), and then to carry through a number of series from the important parts for microscopical examination. By this means the relations of the various cerebral structures and of the pathological lesions can be perfectly preserved and studied. This method can be particularly recommended for tracing degenerations in the motor tract.

If there is a noticeable focal lesion, such as a tumor or hemorrhage, it should be so incised, generally frontally or horizontally, as best to show its relations to the important cerebral tracts and ganglia. In these cases also the best results are obtained by hardening the brain entire in formaldehyde, and later making serial sections for macroscopic study or for carrying through for histological purposes. many cases, however, it is necessary or advisable to examine the lesions in the fresh state. For instance, if it be desired to study the neuroglia-fibers, it is positively necessary to cut out thin slices of fresh tissue and to fix them immediately in

In

the proper solution. Often, too, the lesion cannot be or is not found except on fresh examination, or the clinician whose case it is desires to see at once the cause of certain symptoms. Under such circumstances the more ideal method must be sacrificed, and as much made out of the case as is possible in the condition in which it is left after the examination.

For the routine examination of the brain, to demonstrate

FIG. 9.-First cut in the brain (Nauwerck).

its topography and to bring to light suspected or unsuspected lesions, probably no method is more generally used than Virchow's. The objection most often made against it is that the cerebral cortex is too much cut up. In case, however, it is desired to preserve the cortex or parts of it for microscopic purposes, the longitudinal incisions after the first may be omitted, and the cortical portion, after being separated from the stem, may be cut in any way that seems advisable. In like manner, the brain-stem or any other part