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.

    26/170 (page 20)
    THE LONG TRACTS. The important As has been pointed out in describing the method of building Plane of reference. the model, there is a central mass of fibres, which makes a founda- tion for the reconstruction. It consists chiefly of the long sensory tract to the cortex, that is, the medial lemniscus. In a part of its course it is associated with the posterior longitudinal bundle and certain formatio reticularis tracts. ‘This posterior longitudinal bundle is also a long tract, for it contains fibres both from the cord, and from the midbrain, and relates the nuclei of the eye muscles with higher and lower centres. In a study of sections it does not appear that the long sensory tract has any closer form relation with other structures than the long motor tract. The reconstruction brings out the fact that the pyramidal tract, which is non-medullated at birth, does not mould the shape of other structures. On the other hand, if the form of the long sensory tract (Stratum interolivare lemnisci and lemniscus medialis) is once mastered, all the other structures can be related to it. For this reason the shape of the sensory tract is first de- scribed in considerable detail. It has a characteristic form in each of the three divisions of the model; medulla, pons and midbrain. The central fibre mass is shown best in Plate vii (Stratum interol- ivare lemnisci and lemniscus medialis). For convenience it may be considered divided into two parts, a distal or medulla part (S. i. ].) and a proximal part (L. m.) by a cross-bar of fibres, namely, the corpus trapezoideum. These two parts show a marked contrast both in form and in position. . The distal part consists of a thin sheet of fibres extending the whole length of the medulla, and reaching almost from the dorsal to the ventral surface (Plate v1). It lies close to the middle line in a plane parallel to the raphe (Plate m1). This “ medulla sheet,” as I have named it, shows almost no evidence of being composed of - different groups of fibres. The proximal part, on the other hand, is clearly divided into