GENETIC TYPE AXD THE ENDOCRIXES 361 



although there is similarity in appearance. In the operated 

 animal the upper and lower jaws are about equally shortened, 

 and in addition the upper jaw is set farther back because 

 of a similar arrest in the basicranium, resulting in a shorten- 

 ing- of the upper face; consequently, the lower jaw, though 

 short, projects in front of the upper. In contrast to this, the 

 natural bulldog types may show many different degrees of 

 disharmony between the two jaws because of the independent 

 inheritance of length in each. The lower jaw may be much 

 shorter than the upper, giving the overshot condition, or 

 much longer, as in the undershot condition. In the artificial 

 arrests due to gland removal, both jaws are about equally 

 handicapped. 



The above remarks are not to be misconstrued as a de- 

 preciation of the importance of surgical experiments. These 

 have been very instructive. Our purpose is merely to show 

 the difference between such artificial arrests in growth and 

 those distortions in structure which arise from genetic dis- 

 turbances. 



With such points in mind we may examine the behavior 

 of the head features in the Saluki-Pekingese hybrids. Plate 

 73 shows profile photographs of the two parent breeds and 

 their hybrids at adult age. The Saluki, with typical long 

 slender muzzle, is shown in figure 1, and the Pekingese, with 

 its flat and muzzleless face in figure 4. Measurements and 

 indices of the skulls for these breeds are given in table 1 

 (p. 208). The immature heads of F 2 animals at 5 months of 

 age are shown in plate 74. 



Figures 2 and 3 in plate 73 are heads of F x hybrids, a 

 cream-colored male (tig. '2) and a black and white female 

 (fig. 3). Both have well developed strong muzzles which 

 show very little resemblance to the shortened muzzle in the 

 Pekingese. The male is very slightly undershot ; the female 

 just a little more so. Both profiles show a combination of 

 parental features rather than a similarity to either parent 

 stock. The faces are much shorter and heavier than in the 



