On the posterior lobes of the cerebrum of the quadrumana / by William Henry Flower ; communicated by Dr. Sharpey.

  • Flower, William Henry, 1831-1899.
Date:
[1862]
Catalogue details

Licence: Public Domain Mark

Credit: On the posterior lobes of the cerebrum of the quadrumana / by William Henry Flower ; communicated by Dr. Sharpey. 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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    into the substance of the hemisphere. It must be observed that in the human brain there is some variation in this respect, but the average depth of the calcarine fissure is well illustrated in this example, as also the usual size of the posterior cornu. This ca\ity appears in section as a mere fissure curved round a delicate stratum of white substance, which covers internally the grey matter of the calcarine sulcus, and which constitutes the ventricular surface of the hippocampus minor. In section C no trace of the opening can be discovered. Such is the appearance presented by this portion of the brain, in the highest state of perfection which that organ attains; a condition, however, always the least favourable for studying the morphological significance and true relations of its several parts. The original design, now obscured by special adaptive modifications, can only be traced either by observing the gradual evolution of the same parts from their most rudimentary condition, or by a comparison of similar structures in other animals of simpler organiza- tion. By the first method we learn that while the hemispheres of the brain are mere sacs, and perfectly devoid of convolutions, the calcarine is one of the first of the sulci which appears on the surface (about the fifteenth week, according to Tiedemaxx), and coinci- dent with it, an elevation is seen upon the interior of the ventricle, the future hippo- campus minor. The eminence is, in fact, formed simply by an involution of the wall of the original ventricular cavity, and such portion of this cavity, situated in the posterior lobe, as has escaped being closed in by the growth of the surrounding cerebral sub- stance, constitutes the posterior cornu. The variability of its extent in the human sub- ject, and consequent apparent variability of the hippocampus minor, is well known*. Little physiological importance can, however, be attached to the size of the latter as commonly estimated by the projection into the ventricle. The real amount of cortical or ganglionic neurine surrounding the calcarine sulcus can only be ascertained by an examination of the length, depth, and complexity of that sulcus, and remains unaltered whatever may be the extent to which the cavity of the ventricle is closed: just as the size and form of the corpus striatum would be unaffected by the absence or closure of the portion of the lateral ventricle which lies in contact with it. Such an examination, both in different individuals of the human race, and in the brains of various animals, may supply important data in future investigations concerning the functions of special portions of the grey matter on the surface of the cerebrum. * Many of the variations in the condition of these parts must be ascribed rather to pathological changes than to original conformation. Thus, in aged and debilitated subjects, the posterior cornu is often enlarged, and somewhat funnel-shaped, the calcarine projection being also more or less obliterated, a circumstance arising apparently from gravitation of the intra-ventricular fluid during long continuance of the recumbent posture. In atrophy of the cerebral substance, from whatever cause, attended by an increased size of the ventricular cavities, the change is usually most strikingly seen in the posterior cornu.