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 it is 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 



