20 CHARLES R. STOCKARD 



Among domestic horses there are well known giant and 

 dwarf breeds the powerful, slow-moving, heavy truck horses 

 and the diminutive Shetland ponies. There are also slender 

 greyhound-like race horses. All these animals deviate from 

 the normal size and form of the wild horse. There are, how- 

 ever, no well expressed acromegalic conditions among horses 

 and no large variety of dwarfs and midgets, as occur among 

 dogs and human beings. The domestic horses have in all 

 probability been derived from a less widely hybridized an- 

 cestry than the dogs and this may possibly account in part 

 for the fact that they show fewer divergent and mutant types. 

 It must also be recognized that horses are used by man for 

 working and riding; their selection and breeding have been 

 limited to a fulfillment of these purposes and not to the 

 gratification of a desire to preserve the odd, grotesque or 

 useless. Again, the entire nature of the horse, its size, re- 

 productive qualities and instincts, lacks the appeal for which 

 man has selected the dogs. Should achondroplasia or acro- 

 megaly appear among horses, the individuals so affected 

 would be discarded rather than selected for the establishment 

 of new breeds, nor would the affected animals be reared to 

 maturity for the sentimental or humane reasons that preserve 

 the human freak individuals. 



Domestic cattle probably have a more diverse wild ancestry 

 than does the horse, and they likewise show tendencies toward 

 the production of more divergent and freak types, although 

 these again are not preserved or perpetuated. Exaggerated 

 bulldog types, which are usually non-viable, have long been 

 known to occur among cattle, and their inheritance and 

 glandular conditions have recently been investigated by Crew 

 and. Mohr. However, the large size and slow reproductive 

 processes of cattle, as well as their economic value, prevent 

 extensive experimental study of such material. Several dwarf 

 types of cattle are bred and some of these show mild degrees 

 of achondroplasia. Giant individuals considerably above 

 normal size occur sporadically and are occasionally exhibited, 

 although they are not stabilized by breeding. 



