578 FRANK A. HAYS 
tween the extremes of the ilia was thought to be as easily determined 
as any of the possible body measurements and would represent 
a dimension of breadth in contrast to head length, which might 
be considered a dimension of depth. The iliac expanse was 
therefore used as the second measurement. 
Both measurements were taken Just after weighing on the 
five-day periods beginning at birth and continuing to the ag. of 
ninety days. Steel calipers were used with vernier graduated to 
hundredths of a centimeter. Three independent readings of 
each dimension were taken by removing the calipers and shifting 
the arm after each reading. Readings were put down just as 
read, and care was taken to avoid any tendency on the part of 
the observer to modify readings to make them check with others. 
As a rule, it was possible to obtain readings that varied less than 
0.1 centimeter from each other. An average of the three read- 
ings was taken as the correct reading for each measurement. 
Little difficulty was experienced in securing what was consid- 
ered a correct reading on head length. This was not always 
true for the other dimension. ‘Three factors probably. enter to 
modify this reading: 1, the amount of ‘fill; 2, the degree of 
fatness; 3, the position of the hind limbs. Food and water in the 
alimentary tract seem to bulge the walls of the abdomen to such 
an extent as to often obscure the points of the ium and make 
their exact location difficult. The variability of the feeding 
habits of the rabbit is thus a factor of no little importance in 
connection with the measurement of iliac extremes. Some in- 
dividuals carry much more fat over the ilium bones than others. 
In fat individuals the points of the bones are often greatly ob- 
scured, especially in the younger rabbits. This condition is much 
more common among the smaller and better nourished individuals 
and may prevail to some extent throughout the period of ob- 
servation. There is considerable flexibility in the pelvic girdle 
before the symphisis pelvis becomes bony and firm as the ani- 
mals approach maturity. The ilum, ischium, and pubis are 
also distinct ind more or less flexible in early life. This great 
flexibility causes the position of the hind limbs to be an impor- 
tant factor in modifying the position and the breadth of the ex- 
