Literary Notices. Ixi 



summary of the diencephaloii of Selachii in general. It is advantageous 

 to distinguish a frontal from a caudal segment of the diencephalon. The 

 former is the direct continuation of the basal and lateral portions of the 

 prosencephalon, and is chiefly formed laterally by the pedunculi cerebri 

 and dorsally by the plexus choroideus. At the caudal level the ganglia 

 habenulK, which are composed of two different portions, are seated on 

 the pedunculi of either side. The two habenula; differ considerably in 

 size. The caudal portion is called the pars infundibularis. It begins 

 behind the chiasm and contains in addition to the previously described 

 lobi laterales, a lobus posterior. Ventrad of the latter is formed the wall 

 of the saccus vasculosus. The structure of these parts is minutely de- 

 scribed. 



The following tracts are indicated: i. The basal prosencephalic 

 tract, of which the portion which tirst becomes medullated passes to the 

 infundibulum, the other passes farther caudad. 2. The mantle tract 

 from the mantle of the prosencephalon, which passes ventrad ectad of 

 the optic fibres and decussates caudad of the chiasm. This decussation 

 corresponds with what has hitherto been known as the commissure trans- 

 versa Halleri. After decussating the fibres pass obliquely dorsad over 

 the diencephalon and sink into the basal portion of the roof of the mes- 

 encephalon, beyond which they could not be traced. The mantle bundle 

 is the last of the tracts of pros- and diencephalon to become medullated. 

 Dorsad of it the thick fibres of the decussatio transversa descend from the 

 caudal part of the mesencephalon. These cross caudad and dorsad of the 

 chiasm. 



[The author elsewhere admits that the mantle bundle may not arise 

 in the parts truly homologous of the mantle of other vertebrates.] The 

 caudal portion of the ganglia habenulae are united by the decussatio thai- 

 ami dorsalis. [Commissura habenuhi2, Herrick.] From it ectad the tractus 

 descendens ganglii habenulK hiay be traced downward along the dienceph- 

 alon. Other tracts pass to the prosencephalon and roof of the mesen- 

 cephalon. The fasciculus retroflexus (Meynert's bundle) passes from the 

 frontal portion of the ganglion to apparently unite with its fellow in the 

 interpeduncular. In anticipation of subsequent investigation with better 

 methods the scattered cell masses of the infundibulum were not resolved 

 into ganglia. It is only possible to locate with certainty a corpus genicu- 

 latum beneath the optic fibres on the ectal aspects of the diencephalon. 

 In any case it is necessary to distinguish a central grey of variable thick- 



