GENETIC TYPE AND THE ENDOCEINES 237 



feet. Figure 1 of plate 40, as well as others of this type, 

 would seem to have inherited the upper face and maxilla of 

 the dachshund in association with the abbreviated and curved 

 lower jaw of the Boston terrier. If when such a dog is alive 

 the hand of the observer is placed in the mouth of the animal 

 so as to hide the lower jaw, the head takes on the typical 

 appearance of a dachshund, but if the hand is placed so 

 as to cover the upper face, allowing a view of the lower jaw 

 and chest only, the resemblance is that of a Boston terrier, 

 even to the white hair on the chin and chest. Were the in- 

 ternal chemical environment alone responsible for the patterns 

 of growth, it would be difficult to imagine the lower jaw 

 developing on one pattern while the upper jaw of the same 

 head followed an entirely different mode. Rather does this 

 disharmony between the two jaws appear to be a mosaic 

 condition, with dachshund tissues in the maxilla and Boston 

 terrier constitution in the mandible. 



Be this as it may, the structural disharmony between the 

 upper and lower jaws in these hybrids is extremely pro- 

 nounced, and the resulting functional inefficiency is such that 

 the animal is unable to eat food from a flat surface or shallow 

 plate. Such dogs must be fed from a deep pan so that the 

 abbreviated lower jaw may aid in grasping the food. The 

 growth in length of the face occurs largely after the early 

 weeks of puppy life, and the act of suckling the mother is 

 thus not seriously impaired by these subsequently developed 

 malformations of the mouth. As puppies, these dogs are 

 the same as those of other breeds, all of which have, at birth, 

 a short muzzle and rather flat face with upper and lower 

 jaws of almost equal length. 



The genetic basis for the disproportionately short mandible 

 is definitely transmitted. The male F 2 in plate 40 (fig. 1) 

 was mated with a non-related F x Boston terrier-dachshund, 

 and some of the puppies produced exhibited the same prog- 

 nathous condition of the upper jaw. A male offspring of 

 this mating is shown from two aspects in figures 3 and 4. 

 Several other such matings between the F 2 s and FjS have 



