^6 BULLETIN OF THE LABORATORIES 



dense nucleus of paraxial multipolar cells greatly resembling in size 

 and form the cells of the third and fourth nuclei. This nucleus is 

 situated in the latero-cephalad portion of the thalamus behind the com- 

 missure of the hippocampus. It is related to the epiphysis dorsally 

 and a strong ventral bundle (tcenia thalami) medianly. The whole 

 dorsocephalad part of the thalamus is thickly sown with cells, espe- 

 cially medianly, while a dense clustre of cells of the same sort is situ- 

 ated near the median line a short distance cephalad of the posterior 

 commissure. The axial direction of the last mentioned cells is verti- 

 cal and they give rise to the fibres of Meynert's bundle. The nucleus 

 may be termed nucleus of Meynert's fasciculus. 



The ascending fascicle of the fornix after meeting the anterior 

 commissure passes dorsad to it, entering the septum and becoming 

 enveloped in cubical gray masses lying between the corpus callosum 

 cephalad and the commissure of the hippocampus caudad. The gray 

 mass contains numerous small nuclei. Gradually this mass (and with 

 it the fornix fibres) fuse with the hippocampal commissure. 



The strong tract descending from the habenulae passes laterally 

 and disappears in the region of the peduncular tracts and can be 

 traced no further. 



Comparative data from Didclphys. 



The following memoranda are derived from a series of sections 

 from the opossum. Two principal bundles emerge from near the 

 ventral surface of the medulla, anteriorly. The median pair bound 

 the trigonum and are laterad to the small oculomotor nerve roots. 

 These ventral pyramids of the peduncles pass obliquely cephalad and 

 laterad to a point caudad to the chiasm, where they turn abruptly 

 dorsad. 



The laterad pair of bundles pass oblicjuely dorsad from the latero- 

 cephalad aspect of the medulla to the caudad aspect of the mesen- 

 cephalon. 



The second or sensory bundle continues in its dorsal course as a semi- 

 circular, and finally a circular bundle, to the horizontal plane including 

 the summit of the anterior commissure ; there it begins to break up 

 until, at the level of the corpus callosum and hippocampal commissure, 

 it becomes a reticular formation beneath the testes. The further course 

 of these fibres is obscure, l)ut it a|)pears that they are continued ceph- 

 adal through the thalamus and take part in the decussation of the an- 



