378 
Journal of Agricultural Research 
Vol. XXIX, No. 8 
The relative weight of the skeleton 
shows at first a very slight increase 
attaining a maximum average of about 
16 per cent and then decreasing to 
about 11 per cent for the males and 
about 8 per cent for the females. The 
greater percentage weight of the moist 
ligamentous skeleton in the cockerels 
can not be accounted for entirely by 
the smaller proportion of fat or of re¬ 
productive tract in the male. It must 
be due to other differences in the struc¬ 
ture of the birds. The cockerel is 
characteristically longer-legged than 
the pullet. Moreover, the shape of the 
body is different, as mentioned pre¬ 
viously, the cockerels having a larger 
anterior part of the body, which con¬ 
tains more bony skeleton, while the 
pullets have a relatively larger poste¬ 
rior part of the body which is not so 
well supplied with skeleton. 
left side. In no specimen wxre more 
than eight pairs of ribs found. 
DIGESTIVE SYSTEM 
Digestive tube. —The chart in Fig¬ 
ure 13 shows the growth in weight of the 
entire digestive tube, without contents, 
and the percentage weight, plotted 
against the gross body weight. The 
formulas are: 
r=X°- 62 +0.0053X —4.91 
from 30-1,400 gm. gross body weight, 
7= 0.013(^-1,400)+ 91.74 
from 1,400-2,500 gm. gross body weight. 
7 represents the weight in grams of 
the entire digestive tube, and X, the 
gross body weight in grams. 
Fig. 13—Changes in the absolute and relative or percentage weights of the digestive tube (without 
contents), plotted on gross body weight 
The sex difference in the ligamentous 
skeleton of the chicken is also apparent 
in the relative (percentage) weight 
above 900 gm. in body weight. The 
figures given by Jackson and Lowrey 
(9) for the relative skeletal weight in 
the rat are slightly higher, and show no 
sex difference. Welcker and Brandt 
(28) give 11.69 per cent as the average 
for the two male chickens, 
In making the autopsies on the 100 
chickens, 11 (7 males, 4 females) were 
found with extra ribs. These varied 
from short pieces of bone imbedded in 
the body wall and not connected at 
either end with other skeletal elements 
to complete and normally articulated 
ribs. These extra ribs were found on 
one or both sides of the body. In 
seven males there were seven with ex¬ 
tra right ribs and four with extra ribs 
on the left side. The four pullets with 
extra ribs had four with extra right 
ribs and three with extra ribs on the 
This curve shows a more rapid rise 
at first followed by a second phase of 
slower growth. There is no apparent 
sex difference. The weights of the di¬ 
gestive tube when plotted on age 
form a curve strikingly like that in 
Figure 13, except that the first part of 
the curve is concave on its upper side 
and there is a slight difference in the 
curves for the males and females. In 
this case (as also for other organs) the 
curve for the male digestive tube i§ 
higher, corresponding to the greater 
body weight of the males. The curve 
of the relative or percentage weights 
shows a continuous decrease from about 
15 per cent to about 4.5 per cent. Dur¬ 
ing the first few days there is an increase 
in the percentage weight, but this is not 
indicated in the chart. The percentage 
weights of the empty tube in the nine 
chicks ranging in age from day of 
hatching to 8 days are as follows, in 
order of age; 8, 8.2, 13.6, 12.4, 14, 13.9, 
