42 JOURNAL OF COMPARATIVE NEUROLOGY. 
the dorsal surface of the brain. The only other external mod- 
ification of any note is the absence of either optic nerves or 
optic chiasma. 
Internal Structure of Optic Lobes. 
The optic lobes are normally composed of seven layers 
which are, from outside to inside, as follows: 
(1). A peripheral zone. 
(2). An optic fiber layer from the optic nerve. 
(3). An optic cell layer. 
(4). A deep cell layer. According to Krause this layer 
contains in its outer part the cells which serve as terminal sta- 
tions for the optic nerve, and in its inner sub-layer the end sta- 
tions for the fifth layer (Marklager). 
(5). A deep fiber layer. 
(6). A granular layer. 
(7). The ependyma and its epithelium, which lies next to 
the ventricle of the lobes. 
The optic lobes of Amblyopsis show a marked degener- 
ation. The dorsal walls are not more than one-half or two- 
thirds as thick as in the normal brain. Its contour is so flat- 
tened that the ventricle is almost obliterated (Fig. 8, 16). 
The torus longitudinalis, which in the normal brain is suspended 
in the ventricle in the median line entirely below the layers of 
the lobes is between the lobes and on nearly the same level with 
them. The torus thus forms a commissure connecting the lobes. 
The band of fibers connecting them dips downward in the nor- 
mal brain and crosses to the opposite side through the torus; 
in the degenerate lobe, they cross from one side to the other in 
almost a straight line (Fig. 8, 15). The shrinkage in length 
is shown in the fact that the hypophysis is crowded forward to 
the anterior level of the lobes (Fig. 7, 12). 
The optic nerve of the normal brain is derived from the 
second and fourth layers of the lobes. The fibers of the sec- 
ond layer pass downward on both sides of the lobes and the 
inner ones cross over at the ventral surface where they join the 
fibers of the same layer from the outer side. They then con- 
