GENETIC TYPE AND T1IK EX IK H'llIX KS 



311 



definite modification in its form. This modification is partly 

 genetic, as indicated by other breeds — the Bostor terrier, 

 Pekingese, etc. — and partly a mechanical adaptation to the 

 achondroplasia short skull. 



The baekcross bassethound hybrid shows bassethoivnd 

 values for both the palatal index and the mandibular index. 

 The baekcross bulldog hybrid has a palatal index approaching 

 much nearer the value of the pure bulldog index than do the 



UPPER FACIAL INDEX 



Text-figure 68. Bassethound-English bulldog cross. Each vertical line repre- 

 sents an index based on exact measurements of the skull, and the series of skulls 

 is the same as used for text-figure 65. A, bassethound; B, English bulldog; 

 C, F t ; I), F, ; E, baekcross of F, with bassethound; F, baekcross of F, with 

 English bulldog. 



highest F 2 indices, while the mandibular index in this back- 

 cross hybrid is as completely high as that of the pure bulldog. 

 All these relations are due to the fact that the upper face 

 of the bulldog is more extremely modified than its lower jaw. 

 The top chart in text-figure 68 represents the values for 

 upper facial index in this series of skulls. It will be recalled 

 that the upper facial index (the proportion of nasal length 

 to palatal width) is calculated in a manner the reverse of 



