An atlas of the medulla and midbrain : a laboratory manual / by Florence R. Sabin ; edited by Henry McE. Knower.

  • Florence R. Sabin
Date:
1901
Catalogue details

Licence: In copyright

Credit: An atlas of the medulla and midbrain : a laboratory manual / by Florence R. Sabin ; edited by Henry McE. Knower. Source: Wellcome Collection.

    38/170 (page 32)
    Central ee ass foanbation’ io the model (see page 16). The grouping of structures: in the Medulla oblongata. : in the pons. : in the midbrain. 32 GrRovuPiInGc oF STRUCTURES IN Move for the entire structure. It is clear that in each of the three prin- cipal regions of the model, namely, the medulla oblongata, the pons and the midbrain, this ae bundle, at least the main part of it, has a characteristic shape; in the medulla oblongata it is a me- nae vertical sheet, in the pons, a horizontal sheet, in the midbrain, a lateral obliquely vertical sheet. If now the medulla is considered in the light of its development from the comparatively simple struc- ture of the cord, it will be seen that, as the central canal moves dor- salward to make room for the intrinsic structures of the medulla, the ventral ground bundle, which underlies 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 ventral and a dorsal. The ventral level is characterized by the nucleus olivaris inferior; the dorsal level corresponds to a formatio reticularis 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 pontis. The whole of the structure which character- izes the pons, namely, the pontal nuclei, les 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 dorsalis 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 medialis above the medulla is interesting in connection with the size and central