408 THE TORUS LONGITUDINALIS OF THE TELEOST BRAIN: 



mentioned by Sanders, and he was doubtless in error as to this. His methods did 

 not permit him to distinguish the nerve fibres arising from the cells. He describes 

 the cells as arranged in rows and attached to the radiating neuroglia fibres "some- 

 times by short branchlets and sometimes they are sessile." Sala ('95) described the 

 "cellules nerveuses speciales" of the torus of Tinea as globular or pear-shaped, 10 

 to 14 micra in diameter, and having large nuclei. 



3. Tractus Toro-tectalis. — In the typical bipolar cells the dorsally directed pro- 

 cesses are fine delicate non-medullated fibres. They form fascicles which run dorsad 

 and cephalad to the anterior portion of the torus, where they turn laterally into the 

 tectum, below the dorsal decussation (Figs. 17, 18). Here the fibres of this common 

 bundle separate into two tracts. This division may result from the separation of 

 the two sets of neurites which arose independently from the multipolar cells, or from 

 the spliting of the single process from the cell, into two neurites. 



One bundle so formed, which may be called the tractus toro-tectalis (Figs. 20- 

 25, trt. tor. tct.), continues laterally into the tectum, its fascicles or fibres passing 

 between the fascicles of the dorsaldecsatius on. Within the superficial fibre zone of 

 the tectum the fascicles break up diffusely, ending in contact with the endings of 

 the retinal fibres of the optic nerve (Figs. 24, 25). 



This fibre-tract from the torus to the tectum was first seen by Bellonci ('81, p. 27) 

 who described it as follows: "Von dieser Schicht" (the superficial layer of the tec- 

 tum) "gehen sehr feine blasse Faserbundel aus, welche, nachdem sie parallel der 

 Oberflache des Tectum verlaufen sind, dieselbe in schrager Richtung durchziehen, 

 und sich theils in der darunter befindlichen Region nach dem Tectum zu, theils im 

 Torus longitudinalis allmahlich aufldsen, und zum Theil dazu beitragen, die obere 

 Commissur des Tectum zu bilden." This tract was also seen by Fusari ('87), who, 

 however, did not trace its origin to the torus. It is the same as that which Herrick 

 ('92, '92 a , p. 43) somewhat vaguely described as the "gelatinous tract" and believed 

 to be made up of neuroglia fibres. 



Sala ('95) described the course of this tractus toro-tectalis correctly as "un 

 faisceau de fibres nerveuses qui, se continue lateralement dans le toit optique." He 

 believed, however, that the fibres of this tract passed out from the superficial layer 

 of the tectum into the optic nerve. As Johnston (:01, p. 145) has pointed out, "the 

 fact that they enter the superficial fibre-zone is not sufficient evidence that they go, 

 to the optic nerve." Recent investigations on the origin of the optic nerve fibres 

 (Ram6n y Cajal, '96, p. 104, Fig. 46) show the impossibility of this. 



4. Tractus Toro-cerebellaris. — The other set of fibres already alluded to, which pass 

 from the torus laterad into the tectum, does not traverse the dorsal decussation, 



