An atlas of the medulla and midbrain / Edited by H.McE.K.

  • Florence R. Sabin
Date:
1901
Catalogue details

Licence: In copyright

Credit: An atlas of the medulla and midbrain / Edited by H.McE.K. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    MKDUIJ.A UBLO.NGATA, I'ONS AM) .M IDItK Al.\ on the dorsal surface was really the edge of a sheet wliicli pa.sses vt'iitralward, inward and slightly cerebralward. This sheet is not of unifurni thickness, for its proximal border grows thicker as it passes ventralward; moreover, its surface curves lateralward, thereby in- creasing the distauce between the two peduncles. Reference w-as made in connection with tlie dorsal view, to the flaring out of the distal end of the band. Plate I shows that this portion of the band meets the iiucleiis X. vestibuli superior, a con- nection Avhich is clear in the sections (Fig. 7). On tlie otlier hand the proximal border of the lateral sheet is made of a small bundle of fibres distinguished from the main mass by their direction (Plates III and VII). Opposite this gToup of fibres is a small bundle which crosses from the lemniscus lateralis to the brachium conjunctivum (a on Plates II and YII). The brachium conjunctivum of the model represents not one but at least three different fibre masses. (1) A distal bundle connected with the nuclei N. vestibuli superioris, (2) the main mass of fibres from the coi-pus dentatum which decussate at a ventral level, and (3) a small bundle which runs in the proximal border and decus- sates at a more dorsal level. This group of decussations makes a complicated structure in the model, difficult to describe. It may simplify matters slightly to mention at the outset two moi'phological features. Firet, the main bulk of the decussation of the brachium conjunctivum lies far ventralward and cerebral- ward and thereby comes into relation with the nucleus ruber; sec- ondly, that between the superior peduncles of the two sides in the pons is a wide area in which are situated masses of gi'ay matter belonging to the formatio reticularis gTisea. In Plate VII it will be seen that the decussating mass makes a hollow shell in the floor of the pai-s dorsalis pontis. This shell is open toward the dorsal aspect. Its sides are formed by the curved lateral sheets. The distal bordei-s of these sheets project medialward as a shar]5 ledge and extend A'entralward to a decu.ssation that makes a distal wall for the shell (Plate VII). The sides of the sheet decussate both in the floor of the shell and in its proximal wall. The floor of the decussation is very tlain, for the pi'oximal wall receives the most of the fibres. As has been said, this wall seems to be made of two different masses of fibres (Fig. 44). A simple difference in direc- tion of the fibres at the jioint of deciissation might not be sufficient