284 MOSTLY MAMMALS 
on both sides. That such duplicated antlers are due to a 
splitting during early development is rendered perfectly 
manifest by the head of a fallow-deer figured on p. 855 of 
the Proceedings of the Zoological Society for 1896. In this 
instance it is the right antler which is double throughout its 
length ; but instead of the two divisions of this antler being 
complete in every detail, the front one corresponds only 
with the fore half of the normal complete antler, and vice 
versa. Hence the proof of bifurcation. 
On the other hand, in a three-horned red-deer head in the 
collection of Lord Powerscourt at Enniscorthy the dupli- 
cated antlers of the right side are practically replicas of one 
another; both being somewhat simpler than the normal left 
antler. In this case there is no evidence of bifurcation, but 
the three-horned fallow-deer seems sufficient to demonstrate 
that the origin of the abnormality is the same in both 
instances. If this be the case, there seems no reason why 
additional cranial appendages developed in the four-horned 
breeds of sheep should not have been originally due to 
fission, although no trace of such original splitting can now 
be detected. As a matter of fact, a specimen in the British 
Museum actually shows the occurrence of such a splitting in 
the horns of a ram of this breed. 
Splitting seems, indeed, to be a very common mode by 
which abnormalities are produced. The Museum of the 
Royal College of Surgeons possesses, for instance, the skull 
of a dog in which both the upper tusks, or canine teeth, are 
longitudinally split for about half their length, and there is a 
similar specimen in the British Museum. This splitting is 
clearly due to a partial fission of the crown of the tooth- 
gum. And itis not improbable that a similar fission, carried 
to a greater extent, may explain the condition obtaining 
in the skull of a fox killed during the winter of 1900 by the 
