114 EVOLUTION AND DISEASE. 
The apparent rarity of supernumerary fore limbs, in 
comparison with hind limbs, will be dealt with when 
considering the question of dichotomy as manifested in 
the trunk. 
In cats and dogs dichotomy of the terminal segments 
of the fore and hind-limbs is fairly often seen, and a 
five-legged dog is one of the usual exhibits at a penny 
Fic, 62.—A Dove with an accessory wing, probably 
due to dichotomy, 
monstrosity-show. An uncommon example is repre- 
sented in fig. 63; it isa sheep with an extra fore-limb 
attached to the scapula. The terminal segment is re- 
duplicated. Dissection of the parts seemed to show that 
the abnormal limb was due to dichotomy of the limb 
axis, but this explanation is not altogether satisfactory. 
From supernumerary limbs we may now pass to the 
consideration of what are commonly known as, double 
