598 



modifications of the branchial apparatus and of the ectodermal sense 

 organs in vertebrates. 



D. Bundles of Meynert. 

 In a previous paper ('98) I made a brief reference to the course 

 of Meynert's bundles, stating that the fibres do not end in the Corpus 

 interpedunculare as described by previous workers, but that after 

 decussation they pass on toward the medulla. I have since worked 

 out in detail the further course of these fibres and append a brief 

 description of them. The bundles consist of coarse and fine fibres. 

 The right bundle is much larger than the left and seems to contain 

 more fine fibres. Arrived at the base of the mid-brain the bundles 

 pass ventral to the ansiform commissure and the decussation of the 

 Bindearme, and approach one another in the middle line. Here a 

 considerable number of the fibres decussate, as shown in Fig. 5 i) of 

 the paper referred to. Many of the fine fibres, however, diverge 

 widely. Further posteriorly, and still ventral to the posterior part of 

 the ansiform commissure, the remaining, greater, part of the coarse 

 fibres turn at right angles and decussate. This decussation presents 

 much the same appearance as that described and figured by Van 

 Gehuchten ('94) in the trout. The fibres give ofi' collaterals while 

 decussating, but the individual fibres may be traced with certainty 

 through the decussation and on to their final destination. After 

 decussating, the fibres turn abruptly dorsad, pierce the ansiform 

 commissure, pass around the mesial surface of the Fasciculus longi- 

 tudinalis posterior, and break up into an extremely complicated 

 network of exceedingly fine fibres among the cells which lie around 

 and lateral to the fasciculus. The fibres sometimes divide into three 

 or four branches during or immediately after their decussation, and 

 these, together with some of the collaterals, run to the same 

 destination. The decussation and ending of a few of these fibres are 

 shown in Figs. 9 and 10. A large bundle of relatively fine, non- 

 medullated, fibres ascending from the medulla decussates along with 

 the fibres of Meynert's bundles and ends in the same nucleus. It is 

 shown in Fig. 10, bundle x. The neurites of the cells of the 

 terminal nucleus cross the middle line in the ansiform commissure 

 and join the ventro-lateral tracts. The presence of these neurites, 

 together with the various components of the ansiform commissure, 



1) This figure was wrongly described as a frontal section. It is 

 a horizontal section. 



