Hkkkick, Morpliologv of Nervous System. i6c; 



The olfactory structure comes soon to lie entirely vcntrad to 

 the ala and then disappears. 



In Lepidosteits the relations of the olfactory to the cerebrum 

 are quite different (compare Plate XIII). Here the olfactory 

 lobes extend in the same vertical plane as the cerebrum, but 

 are obliquely applied to the ventral aspect of the hemi- 

 speres, extending well tow^ard the chiasm. The glomerulary 

 structure extends far back, especially mesad, but is overarched 

 laterad by a densely cellular descending portion from the 

 dorsal region of the cerebrum. From this ectal layc- fibres 

 appear to converge to the callosum (Fig. 3, Plate XIII). 



At about the level of the callosum the lateral aspects of 

 the olfactory lobes, beneath the cortical invasion above 

 mentioned, there accumulates a large cluster of olfactory 

 cells which may be traced caudad some distance beyond the 

 olfactory ventricle. 



It will be convenient to begin the study of the cerebrum 

 by reference to the structure of a section cephalad to the 

 chiasm and caudad to the olfactory. 



The transection at this point is somewhat quadrangular, 

 being broadest dorsad. The hemispheres may each be 

 divided, for convenience, into a basal and a lateral portion. 

 The two hemispheres are connected by a small intermediate 

 portion which must be regarded as morphologically equiva- 

 lent to the lamina terminalis, and consequently the cephalic 

 portion of the thalamus. 



The portion of the ventricle adjacent to this thalamus 

 segment difters in the appearance of its epithelial lining 

 from the lateral ventricle. The median walls of the pallium 

 descend to near this level 



The cellular structure of this segment is also unlike that 

 of the cerebrum, consisting of small, clear nuclei with 

 granular contents and pale body, which can rarely be made 

 out in these preparations. 



The basal portion of each hemisphere contains a circular 

 nidulus consisting of the cells which form the caudad con- 



