GENETIC TYPE AND THE EXDOCKINES 



305 



The cranial index is of about the same value in each of 

 the three F! skulls and is very close to the average index 

 for the bassethound. The twenty-one F 2 skulls range in their 

 cranial indices from a low of 56 to a high of 73, which is 

 about the same as the range in the pure bulldog. 



CRANIAL INDEX 



SKULL INDEX 





Text-figure 65. Bassethound-English bulldog cross. Each vertical line repre- 

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

 of skulls was used for both charts. A, bassethound; B, English bulldog; C, 

 F t ; D, F 2 ; E, backcross of F^ with bassethound; F, backcross of F t with bulldog. 



This chart shows, as much previous data have already in- 

 dicated, that the cranial index is not always a highly signifi- 

 cant feature for the differentiation of types among dog 

 breeds. Cranial indices are more variable within certain 

 breeds than they are within others, but there is nearly always 

 considerable overlapping in values among widely different 

 skulls. Part of this variability and overlapping is due to the 

 presence or absence of the sagittal crest; it is difficult to con- 

 trol the effect of this* on index values. In spite of the some- 

 what uncertain importance of the cranial index in the dog 

 skull, we have presented it because of its extensive employ- 

 ment in the study of human skulls. 



