754 
MR. A. SANDERS ON THE ANATOMY OF THE 
In Raja (fig. 12) the cerebellum has the same fundamental arrangement as in 
Scyllium, the four layers, the molecular, the Purkinje cells, the fibrous and the 
granular, are all present. Externally there is a deep transverse furrow formed by the 
molecular layer; in the lateral walls also there are two involutions of the molecular 
layer all followed by that of the Purkinje cells. Internally the ventricle is occupied 
by the four tori of the granular layer, which nearly fill it, leaving only a comparatively 
small cruciform fissure between them. The inferior lobe is well developed, and the 
fold of the molecular layer therein is larger than in Scyllium. 
The total outcome of the difference is that in Raja the cerebellum is more solid and 
massive; there is a larger quantity of material. The molecular layer is more extensive, 
being folded into several furrows, and the granular layer forms larger tuberosities. 
These facts seem to show that the greater activity of life, in conjunction with the 
lighter and less muscular but more agile body, of the dogfish, does not require the 
quantity of nervous substance to start it that is necessary to move the more massively 
muscular and heavier carcase of the sluggish Ray, so that it would appear that 
quantity of muscle requires more nervous activity than quickness of motion. 
The case of Rhina seems to contradict this theory, for with a massiveness of body 
less, certainly, than that of the Rays, but much greater than that of Scyllium, it is pro¬ 
vided with a brain possessing less nervous tissue than that of Scyllium. How to 
reconcile this incongruity is more than I can say. Both in Rhina and Acanthias the 
cerebellum resembles that of Scyllium, except that it is lighter and thinner, and con¬ 
tains a larger ventricle. 
The tuberosities, the arrangement of which has been just described, correspond to 
the granular layer in the solid cerebellum of the Teleostei ; the form here, as has just 
been explained, is that of four, or rather two, discrete longitudinal, more or less 
cylindrical, tuberosities or tori. The fundamental structure is the same both in the 
Plagiostomata and the Teleostei; there is the network of fibrillse (fig. 20), in which 
minute cells are thickly scattered in an irregular manner; these cells are rather larger 
than those found in the corresponding part in the Teleostei; they average 6/x by 4/x, 
and 5/x or 4/x in diameter, their outline is more irregular, and they give off on all sides 
processes which join the network of the neuroglia. 
The arrangement of the network differs somewhat from that found in the 
Teleostei. The general direction of the fibrils is longitudinal; but in addition to 
this the fibrillse form small knots or little masses of neuroglia in which the fibrils are 
inextricably wound together so as to be almost indistinguishable. These knots might 
almost be compared, on a small scale, to the glomeruli of the olfactory lobe. There 
is every gradation of closeness, between some in which the fibrils are scarcely more 
compacted together than in the remainder of the layer, to others which have almost 
the appearance of cells. They are best seen in the Acanthias, in which they are more 
developed than in the other species. The cells are, on an average, of larger size in 
Rhina than in either Acanthias, Scyllium, or Raja, in all of which they are about equal. 
