GENETIC TYPE AND THE ENDOCRINES 207 



DETERMINATION AND COMPARISON OF SKULL INDICES 

 AMONG VARIOUS DOG BREEDS 



The indices of various skull regions permit somewhat more 

 instructive comparisons than do the previously discussed 

 linear measurements, in that indices involve more than one 

 dimension. They express, as a rule, two dimensional rela- 

 tions, these usually involving a width and a length, or trans- 

 verse to longitudinal relationship. For example, the conven- 

 tional cranial index is obtained by multiplying the greatest 

 cranial width by 100 and then dividing the product by the 

 cranial length. Multiplying by 100 enables one to express the 

 index as a whole number rather than a fraction, thus facili- 

 tating comparisons in a series of indices. A high cranial 

 index indicates that the cranium is comparatively wide for 

 its length, while a low figure means a long, narrow cranium. 

 With the exception of the upper facial index (see p. 217), all 

 indices used in the present discussion are to be understood 

 as based on similar calculations. 



A number of indices and measurements for the skulls of 

 pure breed dogs are arranged for comparison in table 1. 

 Measurements have been made on both male and female 

 skulls in most of the breeds represented. Rather consistent 

 differences between the two sexes frequently occur among 

 the pronounced breed types, these suggesting probable endo- 

 crine influence for the differential structural expression. In 

 this table, as well as tables 2, 3, and 4, each group of three 

 values for specific measurements and indices shows first, the 

 average for the females; second, the average for the males; 

 and third (bold-faced type), the average for the breed. The 

 number of animals of each sex which were measured are 

 indicated. It is very difficult with such material as this to 

 have large numbers of measurements for each breed, but 

 probable errors as well as the coefficients of deviation are 

 indicated in the table. 



