402 THE TORUS LONGITUDINALIS OF THE TELEOST BRAIN: 



groups of teleosts. The manifold forms which the torus assumes presents in itself 

 an interesting study in variation, in which it is often possible to correlate closely 

 cause and effect. 



The torus longitudinalis was first observed in the herring, and described by Carus 

 ('14), who believed it to be the homologue of the fornix of higher vertebrates and 

 applied that name to it. Gottsche ('35) subsequently agreed as to this homology, 

 and described it, occurring in somewhat variable form, in a number of species. 

 Fritsche ('78) maintained that the optic lobes of fishes represented the cerebral hem- 

 ispheres, and considered the torus longitudinalis homologous with the fornix and 

 corpus callosum. 



Sanders ('78) in his brief description of this organ also alludes to it as the fornix. 

 He is the first to give any description of its internal structure. He describes the 

 cells as small and spherical, arranged in radiating rows separated by bundles of fibrillae 

 to which the cells are attached by short branchlets. 



Stieda ('68), Bellonci ('80, '81, '82), Mayser ('82), Wright ('84), Auerbach ('88), 

 and Herrick ('91, '92, '93) treat of the optic lobes, but have little or nothing to say 

 of the torus, and nothing whatever of its finer structures. Among the more recent 

 writers who deal with this region the torus longitudinalis is wholly ignored by Fusari 

 ('87), Burckhardt ('94), Van Gehuchten ('94), Neumeyer ('95), Mirto ('95), Haller 

 ('98), Pedaschehko (:01), and it receives mere mention from Ramsay (:01). 



Rabl-Ruckhard ('82, '84), from embryological and comparative anatomical 

 studies, proved that the earlier writers were in error as to the homology of the fornix 

 and torus, and showed the torus longitudinalis to be a structure peculiar to fishes. 

 Later this author ('87), while studying the development of the torus in the salmon, 

 found it to be developed from the roof of the mesencephalon as a longitudinal thicken- 

 ing, by the multiplication of the cells of the inner layer of the tectum. This paper 

 was a brief preliminary announcement, but no later paper has appeared. Wright 

 ('84) briefly described and figured the torus longitudinalis in the catfish. 



Herrick ('91, p. 172) made brief mention of the torus, but added nothing to our 

 knowledge of it. In a later paper ('92, p. 44) he described tracts of fibres running 

 from the torus to the tectum. These he called the " gelatinous tracts " and believed 

 them to be not nerve-fibres but neuroglia. In common with previous observers he 

 did not consider the torus a nerve centre. 



Sala ('95) studied the torus of the young of Tinea vulgaris by the method of 

 Golgi and demonstrated the presence of (1) nerve-cells with characteristic processes, 

 (2) a nerve-net distributed through the whole area of the torus, and (3) ependymal 

 cells. He added greatly to our knowledge of the finer anatomy of the torus, and 



