116 Development of the Veins in the Limbs of Rabbit Embryos 
net with the umbilical vein do not form a well defined vessel and soon 
disappear. Although Hochstetter recognizes this, he refers to the con- 
nection with the umbilical vein as a tibial border vein. Grosser could not 
identify such a vessel in any of his three youngest bats (p. 149). 
The primitive fibular vein as shown in Fig. 2, p. 98, is a vessel read- 
ily comparable with the primitive ulnar vein. Both course along the 
posterior borders of their respective limbs, in which they are the first 
veins developed. They are undoubtedly homologous. In later develop- 
ment, however, they constantly diverge from one another. Even at 14 
days the fibular vein has two small branches which are not matched by 
any belonging to the ulnar vein. One of these, coming from twigs on 
the outer and caudal surface of the leg, becomes the anterior tibial vein, 
An. T. The other which extends mediad toward what at this stage is 
the inguinal line, may be referred to as the “ connecting branch,” c. Db. 
In the more advanced embryo, Fig. 3, p. 100, the same branches appear 
in similar relations. They have become much larger at 14 days 18 
hours, Fig. 4, p. 102. Here the anterior tibial branch has extended 
diagonally down the limb to the dorsum of the foot. The connecting 
branch has sent its twigs into the abdominal wall and the adjoining tibial 
border of the hmb. The primitive fibular vein is still the chief vein of 
the leg. 
In the older rabbit, Fig. 7, p. 107, the differentiation of the toes has 
broken up the distal portion of the primitive fibular vein, which has dis- 
appeared almost to the point where it receives its anterior tibial branch. 
This branch now arises from the interdigital veins on the dorsum of the 
foot and its main trunk appears continuous with the proximal part of the 
primitive fibular vein. The anterior tibial and primitive fibular veins 
together, now constitute the sciatic vein, which is embryologically the 
second vein of the leg. 
The reconstructions to which we have referred agree with Hochstetter’s 
description of the development of the sciatic vein except in one detail. 
They do not show that a part of the primitive fibular vein distal to the 
anterior tibial branch persists as the small saphenous vein. 
In the rabbit of 14 days 18 hours, a third vein of the leg has begun its 
development. This is the femoral vein which terminates in the posterior 
cardinal anterior to the sciatic vein. It advances toward the tibial border 
of the limb. At 17 days, Fig. 7, p. 107, it is seen approaching the ex- 
ternal mammary and the connecting branch of the sciatic vein. In the 
embryo of 20 days, Fig. 8, p. 108, it has anastomosed with both and passes 
down the leg as the posterior tibial vein, Po. T. 
Just as it is questionable in the arm whether the parent vessel should 
