176 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



In his paper on the brain of Salrao and Scylliiun, Haller ('98, p. 514) 

 was unable to arrive at any conclusions as to the relations or meaning 

 of the 'Dachkern.' In his paper on the brain of Emys (:00, p. 277) 

 he claims that the ' Dachkern ' is the analogue of the ' nucleus corti- 

 calis,' and that the axons of the cells join the ' Associationsbahn ' 

 which runs ventrad to the Oculomotor region, where it decussates with 

 the corresponding bundle of the opposite side and is lost between the 

 ventral longitudinal bundles. 



In describing the termination of the optic tract, Houser (:01, p. 125) 

 shows that " the fibres of the stratum medullare profundum pass into 

 the base of the midbrain in two somewhat clearly marked divisions. 

 The inner division is composed of those fibres lying nearer to the cen- 

 tral gray matter from the outset. Some of these have but a short 

 course downward and outward, but the great mass of fibres continues 

 near the median line as a series of intercrossing bundles which are 

 destined to decussate ventral to the aqueduct of Sylvius." 



A comparison of Houser's description and figures with those of 

 Haller shows that Haller's * Associationbahn ' is the " inner division 

 of the stratum medullare profundum" of Houser. It is easy to con- 

 ceive, then, how Haller, having traced the axons into the neighborhood 

 of the stratum medullare profundum, should have been misled as to 

 their destination. 



Edinger (:01, p. 668), in describing in Scj'llium the fibre-tract from 

 the tectum opticum to the cei'ebellum, alludes to ' Dachkern ' as fol- 

 lows : " Seine dicken Markfasern sammeln sich aus der tiefsten Schicht 

 markhaltiger Fasern, welche das Mittelhirndach besitzt, dicht iiber den 

 grossen Zellen des Xucleus magnocellularis tecti, den man gewohulich 

 dem Trigeminus zutheilt indem man ihn dem Mittelhirnkern dieses 

 Nerven, der fur die Sauger ausser Frage gestellt ist, homologisirt. 

 Seine Lage spricht ftir diese Auffassung, dennoch halte ich es fiir durch- 

 aus moglich, dass diesen Zellen die Fasern des Tractus cerebello-tectalis 

 entstammen." 



Houser, having failed to discover the two principal processes arising 

 from the cells of the 'Dachkern,' naturally failed to distinguish the axon 

 and cerebellar neurite. He says (:01, p. 130) : "The axons from the 

 several cells of the same side turn . . . anteriorly, and become associated 

 into bundles, which constitute a fairly well marked tract. This tract 

 extends forward to the anterior limit of the midbrain, where it unites 

 with its fellow from the opposite side, and the united group of fibres 

 emerges from the midbrain roof to penetrate the aqueduct of Sylvius as 



