THE BRAIN OF A FQTAL ORNITHORHYNCHUS. 199 
The Pallium. 
Five distinct layers are recognisable in the pallium (fig. 20). 
These are arranged in the following order—proceeding from 
the surface, and comparing with the layers of the olfactory 
bulb. 
Pallium (fig. 20). Olfactory bulb (fig. 18). 
suence 1. The olfactory ganglion 
(an added layer). 
erlbesmolecule player 7) x carunsen -sntiosede: 2. The nerve-fibre layer (y). 
2, The superficial nerve-cell or “mantle” 
layer (e) 
3. The middle nerve-fibre layer (@) 
4. The deep nerve-cell layer (c) 
Depth evependymal layer {(@) cues ade acacieeent' ee ependymal layer (e). 
pan 
...8. The layer of nerve-cells (6). 
The superficial or molecular layer of the pallium forms 
a clear peripheral band containing only scattered cells and 
nerve-fibres, It is the rudiment of the molecular layer of the 
adult cortex, and also appears to correspond to the ‘ Rand- 
schleir.” In the pyriform lobe and hippocampus (fig. 10) it 
becomes greatly thickened. In the basal regions it does not 
exist as a distinct layer. 
The superficial nerve-cell layer (e)—the mantle layer 
—consists of a very regular stratum of densely packed neuro- 
blasts, from which the most important constituents of the 
cortex develop. 
The middle nerve-fibre layer (d) contains a large 
number of nerve-fibres and scattered neuroblasts. It appears 
to be the ‘ Anlage” of the corona radiata, although in the 
region of the corpus striatum it is separated from the corona 
proper by a large mass of cells. 
The deep nerve-cell layer (c)—the Rolando-cell layer of 
Ludwig Lowe—is more or less intimately joined to the epen- 
dymal layer (a), but a slight interval (b) where the cells are 
not so closely packed indicates the line of separation. The 
destiny of this layer is uncertain, 
