16 BULLETIN OF THE 
The Cartilages of the Tail. 
Plate XIV. Fig. 1. 
Below the vertebre the series of radials of the caudal fin begins con- 
siderably in advance of the fin itself, over the hinder portion of the anal. 
(Pl. XIII. c-c.) Posteriorly they have the appearance of being formed 
by downward growth of the hemapophyses, separation or segmentation 
from which only obtains in twenty-one of the anterior. The lines in the 
sketch, which might be taken as separations in the others, only serve to 
show the course of the vessel enclosed by the transparent cartilage. 
The upper series of the radials of the caudal begins under the extrem- 
ity of the dorsal fin. For a short distance in front, not shown in the 
sketch, the series is separated by a space from the neural intercalaria, 
as if the radials had originated like those of the dorsal and anal, inde- 
pendently, and afterward through downward growth had in the greater 
portion of the extent come in contact with the neural processes. These 
radials and the interneurals are not fused like the radials and hema- 
pophyses. They retain a considerable size at the end of the vertebral 
column. 
The Brain. 
Plates XV. and XVI. 
The brain is very small. Comparatively the amount of fore-brain is 
much smaller than in the higher sharks, Carcharias, Zygeena, and others. 
In outlines and proportions there is great similarity between this brain 
and that of the Notidanide. In both of the genera of that family 
the brain is equally elongate, and the disposition of the nerves is not 
greatly different ; the differences are mainly in details rather than in 
general build. Owing to the softness of the mass, when removed from 
the skull, it collapsed and spread out so that the figures sketched are a 
trifle more broad and flattened than is natural. The condition prevented 
such a removal of the envelopes as was desirable. The olfactory lobe 
is shorter than that of Hexanchus (compare Maclay, Das Gehirn der 
Selachier, Plate II.). The olfactory bulb is similar in shape in these 
genera ; it is a club-shaped expansion with lobules at the end from which 
the nerve distribution takes place. Being broader in front, the hemi- 
spheres taper more toward the hypophysis than is the case in Hexanchus. 
As in the latter, the optic lobes are rounded above and in front, and are 
— when viewed from above — about half exposed. 
