66 JoiTRNAI. OF COMPARATIA-E NEUnOT^OGV. 



Structure. — Passing laterad from the fissura longitudinalis 

 to the ventricle, the fronto-median lobe is composed of three 

 parts : 



I. Bordering the meson, a narrow cell-less fibre layer. 



3. A wider, inner portion containing nerve cells. This is 

 the fronto-fiii'diai/ uidzilus. This niduliis is composed of a 

 large number of irregularly arranged fusiform or flask cells, 

 among which are distributed numerous Deiter's corpuscles. 

 These flask cells are about twenty-five micro-millimetres 

 wide. They stain faintly and have a clear, granular, sub- 

 spherical nucleus and a dense nucleolus. The nucleus is 

 quite large, being at least half as wide as the cell (Plate 

 VIII, Fig. 3). 



3. Bordering the ventricle, a narrow gelatinous layer of 

 closely packed Deiter's corpuscles. 



Iiitra-voitricular Lobe (Plate V, Fig. 6: Plate VII, 

 Fig. ^). — This lobe occupies the middle portion of the 

 mesal division of the mantle. It constitutes that local swell- 

 ing of the mantle which lies ventrad to the fronto-median 

 and occipital lobes. Cephalad and dorsad this lobe is con- 

 nected by a narrow sheet of brain substance with the fronto- 

 median and occipital lobes. This connecting sheet does not 

 contain nerve cells, but it is moderately supplied with 

 Deiter's corpuscles. The mesal boundary of this lobe is 

 formed by the fissura longitudinalis. The majority of the 

 ental boundary is formed by the lateral ventricle, the 

 remainder by the axial region of the hemisphere. 



Transverse sections of this lobe are sub-triangular, while 

 horizontal sections may be either sub-triangular or diamond - 

 shaped. Cephalad and dorsad this lobe is quite narrow, but 

 while passing caudad and ventrad it graduall}' widens. 



Structure. — Like the fronto-median, this lobe is com- 

 posed of three portions: 



I. Bordering the mescni, a dense la\er of slender fusiform 

 cells. These cells are about three micro-millimetres wide 

 and from 13 to 16 micro-millimetres long. Although fusi- 



