Volume 1

Quain's elements of anatomy / edited by Edward Albert Schäfer and George Dancer Thane.

Date:
1895-1898
Catalogue details

Licence: Public Domain Mark

Credit: Quain's elements of anatomy / edited by Edward Albert Schäfer and George Dancer Thane. Source: Wellcome Collection.

Provider: This material has been provided by King’s College London. The original may be consulted at King’s College London.

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    station in a special gi'oup of nerve-cells (upper nucleus of thefillef) at the level of the inferior corpora quadrigemina. Some of the lateral fibres of this middle portion, however, pass to the upper corpora quadrigemina (u^jper fillet), and even extend beyond the superior quadrigeminal region to the subthalamic region (Flechsig), eventually reaching~flie'parieto-occipital part of the cerebraT'Tiem'ispheres by the posterior part of the internal capsule (v. Gudden). Both the upper and lower fillet receive fibres from the antero-lateral columns of the spinal cord, for after hemisection of the cord, degenerated fibres are seen on the same side, both in the lateral fillet of the mesencephalon, where they are mingled with the mass of undegenerated fibres which have been derived from the nucleus gracilis and nucleus cuneatus (see p. 53 and below), and in the bundle of the upper fillet, which enters the superior corpora quadri- gemina ; a few degenerated fibres are also seen in corresponding positions on the oppo- site side. Traced downwards the fibres of the lower fillet pass, as we have seen, a lew by means of the trapezium towards the auditory nucleus of the opposite side, a few to the antero-lateral column of the medulla oblongata and cord (antero-lateral ascending tract), but most are traceable to the anterior column of the medulla oblongata dorsal to the pyramids, and passing across the raphe, proceed as internal arched fibres to the nuclei of the posterior columns, from the cells of which they in all probability arise. To sum up :—The fillet as a whole is composed of ascending fibres, naost of which are derived from the nuclei of the opposite posterior columns of the medulla oblongata, but a few from other sources. The fibres of the antero-lateral ascending tract which enter the fillet may, according to Edinger, be derived from cells of the opposite posterior horn of the spinal cord ; if so, all the fillet-fibres may be regarded as having crossed over from the opposite side, some in the cord, others at the superior or sensory decussation in the medulla oblongata. The fact that they are thus derived is however by no means certain. Superiorly the fillet may be described as being prolonged upwards above the pons in three parts, of which one—the lower fillet—goes to the inferior of the corpora quadrigemina of the same side, a second— upper fillet—to the superior corpora quadrigemina and occipital region of the cerebral hemisphere, and a third, mesial fillet, to the base of the cerebrum through the crusta. DORSAL PART OF THE MID-BBAIN: CORPORA QUADRIGEMINA. As before stated the Sylvian aqueduct is covered on its dorsal aspect by the quadrigeminal lamina, bearing the bodies of the same name. The median part of the lamina is marked by a comparatively wide groove (sulcus lonaitiidinalis, s. sagittalis), shallower inferiorly, Avhich serves to separate the corpora quadrigemina of opposite sides (fig. 77). This grooved surface, which is raised above the level of the upper medullary velum, is connected with the velum by a small median strand of longitudinal fibres termed the framilm veli (fig. 77,//-). In front of the upper (anterior) pair of corpora quadrigemina the gi'oove is interrupted by a transverse white prominence—the posterior commissure ; but both this and the upper end of the median groove are in thenatural condition concealed by the pineal body {p), which projects backwards and downwards from the posterior wall of the third ventricle and rests between the upper pair of quadrigeminal bodies. A well-marked narrow transverse groove {sulcus transversus) which commences a short distance from the middle hue, and is curved round the lower border of the upper tubercle, separates this from the lower tubercle of the same side. The corpora quadrigemina are two pairs of rounded eminences which are mainly composed of grey matter, although covered externally by and containing in their interior many white fibres. The upper or anterior tubercles (fig. 77, c.q.s.)