The relative position of parts must inevitably be greatly modified if further incisions are made. Meynert's method of opening the brain is entirely different from that which is usually adopted, but is followed by many specialists in mental disease. The chief end to be gained by this method is the determination of the weight of each of the three great portions of the brain (brain-covering, brain-stem, cerebellum) taken separately. The pia mater is not removed, but the brain being placed with its base upwards, the islands of Reil are dissected away from their attachments so freely as to allow the three fissures which bound each of them to be clearly seen. <Callout type="important" title="Key Method">Meynert's method focuses on determining the weight of different brain parts separately.</Callout> The pia over the great transverse fissure of the brain is then detached laterally and behind so that on raising the medulla oblongata, pons, and cerebellum, the descending cornu of the lateral ventricle may be directly exposed. The anterior portion of the parietal lobe is next grasped, drawn somewhat backwards, and its connection with the stem cut through by keeping close to the posterior furrow of the island of Reil externally, and to the outer wall of the descending cornu internally. The island is then separated from its base by holding the knife nearly horizontal, and cutting through the outer limiting furrow, care being taken to keep close to the outer angle of the lateral ventricle formed by the corpus callosum and the great cerebral ganglia, which may readily be seen by lifting the cerebral stem. These cuts having been made on both sides, the knife is passed into the longitudinal fissure, and a horizontal section (parallel with the orbital surface of the frontal lobes) and about three centimeters deep, is made through the depression just in front of the anterior perforated space, then following the anterior furrow of the island of Reil, with a slight curve concave outwards until the cut previously made through the outer furrow is met. The stem and cerebellum are now raised and made tense, the pillars of the fornix and the septum lucidum are cut through from below, just in front of the anterior commissure, and finally the brain-stem is completely detached by separating from below the remaining adhesion in front of the corpus striatum. This portion is readily separated from the cerebellum by cutting through the several processes connecting the two. The following figures are Meynert's, and are based on the examination of 157 bodies at the Vienna Insane Asylum. The average weight of the whole brain between the ages of twenty and sixty-nine years, is 1,296 grams in the male, the maximum being in persons between forty and fifty years of age, and 1,169 grams in the female, the maximum being in those between fifty and sixty years of age. The average weight of the brain-covering is 1,018 grams in the male, 917 in the female ; of the brain-stem 143 grams in the male, 129 in the female ; of the cerebellum 135 grams in the male, 123 in the female. Morbid Conditions of the Brain. Of the local lesions which are met with in different portions of the brain, the first to claim our attention is — 1. Haemorrhage. This may be of large extent or punctate — sometimes incorrectly called capillary — though the two forms are very often coexistent, and the punctate variety is almost always found in the vicinity of large haemorrhages. If the bleeding be of traumatic origin it is very apt to be seated directly opposite the point where the injury was inflicted (haemorrhage from contre-coup), while this point is absolutely or nearly free from haemorrhage. Those haemorrhages which are due to disease of the vessels are found chiefly in the great ganglia where the arteries ascend into the brain from the fissure of Sylvius, and often break through into the lateral ventricles. Large cells filled with red blood corpuscles are often found in these apoplectic clots on microscopic examination, and are merely white corpuscles with red ones incorporated in them ; they are easily found by tearing apart a small portion of the clot in a one per cent solution of common salt, but water and acid should not be used for the reason that they destroy the coloring matter of the red cells and render them indistinct. 2. Softening of the brain (mollities cerebri) is so often dependent on haemorrhage that it, in its various forms, comes naturally next in order. The form of softening which is generally qualified as 'red' results from partial breaking down of portions of cerebral substance between and about haemorrhages, and acquires its color — which later is somewhat brown — from admixture with blood. Red softening may be of traumatic, embolic, or inflammatory origin ; and it is very often impossible, especially in the later stages, to arrive at the exact mode of origin from the local appearances alone, though sometimes the history of the case and the condition of other organs or parts throw light upon the question.
Key Takeaways
- Meynert's method for brain dissection and weight determination is crucial for understanding brain structure.
- Haemorrhages can be of traumatic or vascular origin, often leading to red softening in the brain.
- Softening of the brain can occur due to various causes including inflammation and embolism.
Practical Tips
- Use a one percent solution of common salt for microscopic examination of blood clots to preserve cell integrity.
- Recognize that traumatic haemorrhages often appear opposite the injury site (contre-coup).
- Understand that red softening in the brain is usually due to partial breakdown around haemorrhages.
Warnings & Risks
- Avoid using water or acid when examining blood clots under a microscope as they can destroy cell coloring.
- Be cautious of punctate haemorrhages near larger ones, which may indicate underlying vascular disease.
Modern Application
While the detailed anatomical and pathological descriptions from this chapter are foundational for understanding brain injuries and diseases, modern medical imaging techniques such as MRI and CT scans have largely replaced manual dissection methods. However, knowing these historical techniques can provide valuable context for interpreting current diagnostic findings.
Frequently Asked Questions
Q: What is the purpose of Meynert's method in brain dissection?
Meynert's method aims to determine the weight of each major portion of the brain separately, providing insights into its structure and pathology.
Q: How does red softening occur in the brain?
Red softening occurs when portions of cerebral substance break down around haemorrhages, mixing with blood to form a reddish-brown mass.
Q: What are some common origins of brain haemorrhage?
Brain haemorrhages can be traumatic or due to vascular disease. Traumatic haemorrhages often occur opposite the injury site, while vascular ones tend to appear in great ganglia near the fissure of Sylvius.