220 bulletin: museum of comparative zoology. 



Bellonci ('81, p. 27, Tav. 11. Fig. 1 (b) ), who described it as follows: 

 " Von dieser Schicht [the superficial layer of the tectum] gehen sehr 

 feine blasse Faserbiiudel aus, welche, nachdem sie parallel der Ober- 

 flache des Tectum verlaufeu sind, dieselbe in schrager Richtung durch- 

 ziehen, und sich theils in daruntei' befindlichen Region nach dem 

 Tectum zu, theils ini Torus longitudinalis allraahlich auflosen, und zum 

 Theil dazu beitragen, die obere Commissur des Tectum zu bilden." ^ 



This tract was also seen by Fusari ('87, Taf III. upper end of figure), 

 who, however, did not trace its origin to the torus. It is the same as 

 that which C. L. Herrick ('92, p. 43, Fig. 9) somewhat incorrectly 

 described as the 'gelatinous tract,' and believed to be made up of 

 neuroglia fibres. It is identical with the tractus toro-tectalis, which 

 I have described in teleosts. Sala believed 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 (S. Ramon y Cajal, '96, p. 104, Fig. 46) show the impossibility of 

 this. 



Of the other branches which Sala found to come off from the torus- 

 cells, one was similar to that already described, but could be followed 

 only a short distance into the tectum (Fig. L, ax."). This is evidently 

 the incompletely impregnated neurite which goes to form the tractus 

 tecto-cerebellaris. The third process, the greatest in diameter, he found 

 to take an irregular course and to terminate freely a short distance from 

 the cell in a slight enlargement (Fig. L, ax.'"). This, it is quite evi- 

 dent from its way of ending, and failure to establish relations with other 

 elements, is due to its incomplete impregnation. Sala makes no attempt 

 to explain the relations or functions of this process. I think there can 

 be little doubt that this is the partly impregnated axon of the cell, 

 which runs mesad and cephalad to emerge into the ventricle either in 

 the ventral fissure of the torus, or anterior to the posterior commissure. 

 A careful study of his figures shows that this process is usually directed 

 toward the median plane (Fig. L). Unfortunately all his figures are of 

 transverse sections, and evidently from the posterior part of the torus. 



1 According to Bellonci the optic nerve-fibres end in the outer layer of the 

 tectum, where tliey are lost in the fine net througli which they are in direct 

 connection with tlie long processes of the nerve-cells of the inner layer of the 

 tectum. In another paper Bellonci ('80) gave numerous figures (Figs. 5, 11, 18, 

 28, 32) of cells from the optic tectum whose finer dendrites anastomose, in some 

 cases (Fig. 18) anastomosing with the ends of the optic nerve-fibres. 



