Texture of the Nervous System of Man and the Vertebrates by Santiago Ramón Cajal

Author:Santiago Ramón Cajal
Language: eng
Format: epub
Publisher: Springer-Verlag Wien 2012
Published: 2014-12-14T16:00:00+00:00

In the head of the dorsal horn and bordering region of the substantia gelatinosa, there are other small longitudinal bundles of myelinated fibers, which are seen in continuity with sensory collaterals when followed in longitudinal sections. These myelinated bundles (Fig. 124B) surely correspond to the system of longitudinal fibers of the dorsal horn, designated by Kölliker as the longitudinal fascicle of the dorsal horn, According to Lenhossék, such fibers would be of sensory radicular nature, which instead of bifurcating in the midst of the dorsal funiculus, would divide in ascending and descending branches in the very territory of the dorsal horn6. We could not confirm such an arrangement. We have always thought to have seen in many preparations that the mentioned longitudinal fibers are the continuation of either thick sensory collaterals, or ascending or descending branches of the bifurcation of ordinary radicular fibers. In Fig. 124a, b, we reproduce some of these bundles, the position of which varies according to the sections; for example, the same bundle which in one section runs obliquely through the substantia gelatinosa, appears in another in the ventral border of the latter, or in the head of the dorsal horn. Because the course of these small bundles is not transversal, but oblique, bending further to become vertical, it is well understandable that sometimes they appear cut transversely and other times lengthwise. As it happened with the displaced packets of the dorsal horn bundle, the arrangement of these thick vertical collaterals is plexiform, one small bundle separating frequently to join others (Fig. 125E).

Longitudinal packets formed by sensory collaterals and terminals, as well as those represented by displaced bundles in the dorsal horn system (fasciculus proprius of the lateral funiculus), emit numerous collaterals during their longitudinal course. Sensory branches ramify in the head and central portion of the dorsal horn (Fig. 124b); some even reach the substantia gelatinosa. Those of displaced bundles, much more numerous, run in all directions and end by arborizing in the base and center of the dorsal horn, i.e. in a more ventral plane than collaterals of sensory longitudinal bundles (Fig. 124d, c).

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