TiKMCK, Morplio/oo'v of the Avian Brain. 67 



form in shape, these cells stain densely and have a dense 

 nucleus. They lie in a fibre tract and have their major axes 

 parallel to the meson and to the base of the prosencephalon 

 (Plate VIII, Fig. 11). 



2. A wider, inner portion, containing nerve cells. This 

 is the intra-ventricular iiidnhis. It is composed of a large 

 number of irregularly arranged gibbous, fusiform or flask 

 cells, among which are distributed numerous Deiter's cor- 

 puscles. These fusiform cells are about three micro- 

 millimetres wide and from 9 to 13 micro-millimetres long. 

 They stain faintly and have a large, clear, granular sub- 

 spherical nucleus and a dense nucleolus (Plate VIII, Fig. 11). 



3. Extending along the ventricle, a narrow border of 

 slender densely stained fusiform cells. Histologically these 

 cells resemble the cells that extend along the meson. They 

 vary in length from 10 to 13 micro-millimetres. Like the 

 cells along the meson, their major axes are parallel to the 

 meson and to the base of the brain. 



Occipital Lobe. — This lobe constitutes the caudad portion 

 of the mesal division of the mantle (Plate \T, Fig. 3; 

 Plate VII, Fig. 5; O. L). It is the development of this lobe 

 which causes the local swelling in the caudad portion of the 

 mesal wall of the ventricle. The mesal boundary of this 

 lobe is formed by the fissura longitudinalis, the lateral by the 

 ventricle, while the caudad is coincident with a portion of the 

 caudad surface of the hemisphere. 



Horizontal sections of this lobe are crescent-shaped, 

 while transverse sections are sub-triangular. Dorsad this 

 lobe is quite wide, but while passing ventrad it gradually 

 becomes narrow. 



Structure. — This lobe also consists of three layers: 



1. Along the mesal l^order there is a narrow cell-less 

 layer containing fibres. 



2. An inner portion containing nerve cells. This is the 

 occipital iiidxlns. It consists of a large number of fusiform 

 or flask cells, among which are distril)utcd numerous Deitcr's 



