GENETIC TYPE AND THE ENDOCRINES 301 



shown in plate o6 where the three posterior premolar teeth 

 are set at right angles to the normal position seen in the 

 accompanying long skull. 



The mandibular premolar teeth occupy 80 per cent of the 

 length of the mandibular premolar region in the bassethound, 

 which is about the same proportion as for the upper jaw. It is 

 a surprising- fact to find that the premolar teeth in the man- 

 dible of the bulldog occupy an even lower percentage of this 

 region, about 72 per cent, than they do in the bassethound. 

 The teeth of the bulldog are not so large and strong as those 

 of the hound. 



The peculiar phenomenon of the crowding together of the 

 premolar teeth in the upper jaw of the bulldog and the free 

 spacing in the lower jaw is due to the fact that the mandible 

 in this deformed skull is much less reduced in length than 

 is the upper face and maxilla. Judging from the conditions 

 found in other short faced breeds, to lie discussed later, the 

 mutations which shortened the upper face and maxilla of the 

 bulldog have not progressed to a point where the mandible 

 is correspondingly shortened. 



The third column in table 4 represents the average values 

 for the skull characters of three F, bassethound-bulldog hy- 

 brids. In genera] the indices and proportions for the F x 

 skulls are between the values of comparable features in the 

 two parent stocks, but in all cases where the indices of the 

 bulldog and the bassethound differ considerably, the I\ falls 

 much closer to the bassethound. For example, in the skull 

 index, palatal index and snout index, the F x values are each 

 about ten above the bassethound and, respectively, 36, 47 and 

 97 below the same indices for the bulldog. Taking average 

 indices for comparisons between F 1 hybrids and the parent 

 stocks is a fair procedure, since the Fj animals are almost 

 as uniform in type as are the pure breeds, this uniformity 

 of the F t hybrids being proof of the purity of the parent 

 stocks. If the parent stocks are not largely homozygous for 



