Some observations on the fiber connections of the di‐ and mesencephalon in the cat. Part III. The supraoptic decussations

Although many communications dealing with these interesting extra-visual crossings have appeared in neurological literature during the last 80 years, little general agreement appears to prevail concerning the origin, course, extent and destination of these fiber tracts. This lack of agreement may be due partly to the fact that attempts to trace these fibers were generally made with normal material, an undertaking exceeding the possibilities offered by such methods. It is, however, possible to throw light on the question with the aid of suitably placed lesions and the Marchi technique, and with material cut in various planes, at any rate as far as coarse or medium-sized elements are concerned. The present study, based upon Marchi stained cat series, has shown that two crossings can readily be demonstrated in this species, a dorsal crossing (corresponding to Ganser 's supraoptic decussation) made up of coarse fibers which appear to become gradually finer or to give rise to fine collaterals towards their termination, and a ventral crossing (corresponding to Meynert 's and possibly also to Gudden's supraoptic decussation) made up of medium-sized or fine elements. The ventral crossing, in contradistinction to the dorsal crossing, conveys fibers running in opposite directions, that is to say, two systems, and possibly also a third consisting of extremely fine ele-

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