74 BULLETIN OF THE LABORATORIES. 



matter. At this level, too, the tracts from Meynert's bundle apparent- 

 ly enter a small, dense interpeduncular nucleus between the third 

 nerve roots and somewhat caudad to them. A large nucleus, (Steida's 

 nucLus pcdicicuhjriti ,) laterad to the third root tracts, and another near 

 the median line, nudens inter pcdunciilaris, to which the fibres of Mey- 

 nert's bundle can be directly traced, are also visible (Fig. 3, Plate IX.) 

 Compare Plate X, Fig. i. 



Longitudinal vertical sections through the corpora quadrigemina 

 at the locus of the third root, are especially instructive as to the rela- 

 tions existing between the third, fourth and other nuclei. (Plate X, 

 Fig. I.) The figure sufficiently illustrates the chief peculiarities. The 

 nucleus of the third lies chiefly below and laterad from the strong me- 

 dian ascending tract and is largely involved in its fibres. The fourth 

 nuclei are composed of entirely similar cells lying in a group caudad 

 and dorsad to the previous nuclei and lying above the ascending tract 

 and near the sides of the floor of the aqueduct. The tracts of IV are 

 seen as two or three circular sections (tr. IV.) 



The descending fibres of what is apparently Meynert's bundle can 

 be traced to a point near the entrance of the third nerve. A strong 

 bundle (tr.) from the prominence immediately in front of the outer 

 passes obliquely caudad and mesiad. 



The third nerve arises by a number of very small roots which sub- 

 divide on entering the substance of the pes into still smaller strands. 

 The course of the fibres can be easily followed dorsally and caudad to 

 a considerable nucleus a little ventrad from the aqueduct. In trans- 

 verse section the outline of this nucleus is triangular and consists of 

 two indistinctly separated i)ortions, a smaller (dorsal) portion and a 

 larger ventral mass, from the base of which the fibres radiate ventrad 

 to the tracts through a white zone surrounding it. The centre of the 

 nucleus lies dorsal to the anterior edge of the pons. 



Ventrally and a little laterad is the larger nucleus, the cells of 

 which are in some res]jects similar, but average rather larger, (Plate 

 IX, Fig. 3, 112) but from it no fibres can be traced to the tracts of III 

 which latter, in converging toward the nucleus proper at the median line, 

 in part jjass through the substance of this cluster. This peduncular nucleus 

 is remarkable in that its cells are exceedingly irregular and wrapped 

 about the strands of the longitudinal tract. These many-branched cells 

 lie in angles of decussating fibres, and like similar cells of the ventral 

 cornua of the cord, send off fibres to the several tracts. 



