440) THE DEVELOPMENT OF THE CHICK 
with the ventral posterior border of the ilium, and the pubis, 
except at its anterior and posterior ends, with the free border 
of the ischium. 
The spina iliaca, a pre-acetabular, bony process of the ilium, 
requires special mention in- 
asmuch as it has been inter- 
preted (by Marsh) as the 
true pubis of birds, and the 
element ordinarily named 
the pubis as homologous to 
the post-pubis of some rep- 
tiles. There is no evidence 
for this in the development. 
The spina iliaca develops as 
a cartilaginous outgrowth of 
the ium and ossifies from 
the latter, not from an inde- 
pendent center (Mehnert). 
The Leg-skeleton. The 
skeleton of the leg develops 
from the axial mesenchyme, 
which is at first continuous 
with the primordium of the 
pelvic girdle. In the process 
Fia. 249. — Photograph of the skeleton of chondrification it seg- 
of the leg of a chick embryo of 15 days’ ments into 4 larger number 
1 > ‘ 1 IpaANnara r » Qe 7 » . 
incubation. Pre pared by the potash of elements than: 4ounaen 
method. (Preparation and photograph 
by Roy L. Moodie.) ; 
1, Tibia. 2, Fibula. 38, Patella. 4, suppressed and others fuse 
Femur. 5, Ilium. 6, Pleurocentra of toeether. The digits erow 
sacral vertebrie. 7, Ischium. 8, Pubis. Le: ; a 
9, Tarsal ossification. 10, Second, third, out from the palate-like eX- 
the adult, some of which are 
and fourth metatarsals. 11, First meta- pansion of the primitive 
tarsal. I, IH, III, IV, First, second, third, ; ; : : 
and fourth digits. limb in the same fashion as 
in the wing. In general the 
separate elements arise in the proximo-distal order (Figs. 242 and 
249). 
The femur requires no special description; ossification begins 
on the ninth day. 
The primordium of the fibula is from the first more slender 
than that of the tibia, though relatively far larger than the adult 
