380 «^0^1° F. Holm 



part of the Ganglion interpedunculare, the majority bend horizontally 

 round the ganglion and decussate behind it. In the Elasmobranches 

 Edinger (7) finds the two fascicles equally strong and that they 

 end in the Gang, interpedunculare, where the fascicle from one side 

 should join with that from the other. Hallee (17) finds that the 

 Fasciculus retroflexus obtains most of its fibres from the ganglion 

 on the same side, but a small part is derived from the posthabe- 

 nular region. 



In Myxine there are two distinct different fasciculi, as may be 

 easily seen in horizontal sections, where they present themselves as 

 two small round discs placed one each side of the middle line. As 

 the Ganglia hab. are placed one before the other the two fascicles 

 run somewhat differently in the beginning. 



The anterior Fasciculus retroflexus springs from the inner an- 

 terior part of the Ganglion habenulae anterior and passes obliquely 

 and caudally along until it arrives below the Commissura posterior; 

 here it bends and runs in a vertical direction (Fig. 16) towards the 

 base of the brain. 



The posterior fascicle springs chiefly from the inferior part of 

 the Ganglion habenula pos. and passes in nearly straight line ven- 

 trally. In the lower half of their tract the two fascicles run parallel. 

 They pass close to, and part of their fibres pierce, the Commissura 

 ansulata in the same manner as described by Mayser in the Te- 

 leostei. 



Haller states, as before mentioned, that the fascicles in Elas- 

 mobranches and Teleosts should receive a small part of their fibres 

 from the posthabenular region, but in Myxine I have been unable 

 to find any similar arrangements. Part of the fibres of the fascicles 

 decussate before entering the basal part of the Mesencephalon, »De- 

 cussatio superiori fasciculorum retroflexorum« and the two bundles 

 separate and run laterally one each side of the Ganglion interpedun- 

 culare (Fig. 8) towards the ventral surface of the brain, where they 

 bend in a caudal direction. Some of the fibres seem to continue 

 straight down into the Medulla, but the majority decussate after a 

 little while and are lost amongst the cells in the base of the brain. 

 This last decussation I call »Decussatio inferior! fasciculorum retro- 

 flexorum« to distinguish it from the former. 



The Tectum mesencephali has connection caudally with the 

 Medulla oblongata et spinalis through the Tracti tecto-spinales et 

 bulbares. These mighty strokes run along ventrally to the central 



