On the commissures of the cerebral hemispheres of the Marsupialia and Monotremata as compared with those of the placental mammals / by William Henry Flower.

  • William Henry Flower
Date:
[1865]
Catalogue details

Licence: Public Domain Mark

Credit: On the commissures of the cerebral hemispheres of the Marsupialia and Monotremata as compared with those of the placental mammals / by William Henry Flower. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    above, with a thickened posterior end (E) turned somewhat downwards, and a distinct genu (C) and rostrum (D) in front. The latter has a smaller proportional development than in the human brain. On the other hand, the slightly projecting posterior fold observed in the human corpus callosum is prolonged forwards as a thin layer of transverse fibres (N) arching across the under surface of the longitudinal fibres of the fornix, and ending in no abrupt edge in front. The difference in the form and extent of this part of the great transverse commissure may be clearly seen to depend upon the difference in the form, and more extensive proportions of the parts that have to be brought into rela- tion to each other by it, viz. those forming the inner wall of the descending cornu of the lateral ventricle. At a considerable distance below the anterior part of the corpus cal- losum the small anterior commissure (F) is seen, with the wide septal area (G) in front of and above it. The portion of this part to which the term “ septum lucidum ” can be applied, is reduced to a small strip beneath the anterior third of the corpus callosum, exactly defined below and in front by the extent of the rostrum of that body. The greater part of the septum is formed by a thick layer, consisting of a great development of the precommissural fibres of the fornix, associated with much grey matter. The small white column (L) of the fornix is seen passing down behind the anterior commissure. The ventricular aperture is less regularly curved than in man, being bent almost at a right angle. Above and behind it is seen a broad corpus fimbriatum (M), behind which the abrupt termination of the cortical substance of the hemisphere in the fascia dentata (P) is very distinctly seen. The regularly curved hippocampal sulcus (Q) ends beneath the hinder end of the corpus callosum, the grey matter of the fascia dentata being con- tinued superficially round its extremity into that of the next succeeding gyrus. In the transverse section (Plate XXXVII. fig. 2), at the bottom of the deep longitu- dinal fissure, is seen the corpus callosum (B), a transverse white band of moderate thick- ness, and slightly arched upwards externally, where its fibres radiate out in the medullary substance of the hemisphere. The anterior commissure (F) is readily recognized near the lower part of the section. The cavities of the lateral ventricles are somewhat tri- angular in form and bounded above by the under surface of the corpus callosum, towards the middle line by the septum, and externally by the corpora striata. The septum obviously consists of two halves, one belonging to each hemisphere, but more or less joined together in the middle line. The upper part (septum lucidum) is extremely thin, and here the absence of union between the two halves allows the existence of a minute cavity, the fifth ventricle. The lower and larger part is very thick, with rounded outer surface. It contains much grey matter, with white longitudinal fibres externally. Within it, near the middle line, on each side, can be seen two bundles of white fibres, standing nearly perpendicularly and slightly diverging from each other below; they are the upper part of the columns of the fornix. The most essential deviations in the commissures of this brain from those of Man con- sist in the reduction of the rostrum of the corpus callosum and the septum lucidum, and the augmentation of the inferior thick part of the septal area and of the psalterial fibres.
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