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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    MICDUU.A ()liI,().\(i.\TA, I'ONS AM) MIUHUAIN ii liitcnil ()l)li(in('ly vertical sli(;et. If now the iiicdulla is considered in the light of its development from the comparatively .sim])le struc- ture of tlie cord, it will be seen that, as the central canal moves dor- salward to make room for tiie intrinsic structures of the medulla, the ventral ground bundle, which un(lerli(>s the canal, becomes enormously developed so as to form the medulla sheet. This me- dulla sheet, indeed, represents far more than the ventral funiculus, for it is made up of fibres from the lateral and dorsal funiculi as well. Indeed, at the beginning of the medulla oblongata, almost the entire dorsal funiculus passes by means of secondary neurones, arcuate fibres, either dorsally to the cerebellum or ventrally into the medulla sheet. This change is interesting in connection with the fact that the cerebellum develops from the dorsal wall of the neural tube at this position according to the work of His. About this vertical sheet can be grouped all the other structures of the medulla oblongata. Just ventral to it, lies the pyramidal tract; while the region lateral to it can be divided into two levels, a ven- tral and a dorsal. The ventral level is characterized by the nucleus olivaris inferior; the dorsal level corresponds to a formatio reticu- laris area which is bordered by the roots of the cerebral nerves and their nuclei. In the pons, the central fibre mass makes a complete floor for the pars dorsalis ]3ontis. The whole of the structure which character- izes the pons, namely, the pontal nuclei, lies ventral to the sheet; while on the other hand, all the structures, which more or less cor- respond to the upward continuation of the spinal cord, lie dorsal to it. This pars doi-salis pontis is composed chiefly of formatio reticu- laris. It receives (1) the middle portion of the proximal subdivi- sion of the central fibre mass, and (2) a mass of fibres from the formatio reticularis of the medulla oblongata. The brachium con- junctivum, or superior cerebellar peduncle, passes through it. The midbrain structures in turn can be grouped around the cen- tral fibre mass. The lateral course of the lemniscus mcdialis above the medulla is interesting in connection with the size and central position of the red nucleus. In the ventral region of the midbrain are the substantia nigra and nucleus ruber separated from one another by the lateral capsule of the red luicleus and the lemniscus medialis, while dorsal to the red nucleus is a fornuitio reticularis area. This area is bounded laterally by the lemniscus superior
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