114 Development of the Veins in the Limbs of Rabbit Embryos 
because “attended by several venous twigs of nearly the same caliber, 
and only shortly before its termination is it recognizable as a distinct 
(stiirkeres) vessel” (p. 24). In a 13-day rabbit the radial vein had dis- 
appeared, “since it had been but imperfectly marked out.” Similarly 
Grosser found a radial vein emptying into the anterior cardinal close to 
the ulnar vein, in the youngest bat which he studied (484 mm.). In the 
next stage (614 mm.) it had vanished (p. 186). An examination of 
rabbits of 12 and 121% days, together with younger ones in the Harvard 
Collection, shows that the first vein of the arm develops along its ulnar 
margin, extending distally around the border to the radial side. Small 
and variable vessels such as Hochstetter described as a radial vein may 
occur, as shown in Fig. 1, p. 97, but they do not form a structure com- 
parable with the primitive ulnar vein. The latter may be called the 
primary vein of the arm. 
The rabbit of 14 days, Fig. 2, p. 98, presents the condition described 
by Hochstetter in embryos of 13 days. The primitive ulnar vein has 
acquired a new outlet ventral to the brachial plexus, so that, by the per- 
sistence of the original dorsal termination, most of the plexus and the 
brachial artery are surrounded by a loop of vein. In the following rab- 
bit, Fig. 3, p. 100, the ventral outlet of the ulnar vein is the chief one. 
This specimen shows a smal] vessel extending from the external jugular 
vein toward the radial border of the arm. 
The next embryo, Fig. 4, p. 102, is considerably more advanced. The 
dorsum of the hand, which was previously its external surface has rotated 
and become anterior; the arm isin pronation. The differentiation of the 
fingers is indicated by the sinuous terminal border of the hand, and by 
shallow interdigital depressions on its dorsum. Beneath these, inter- 
digital veins have been formed, probably from branches of the primitive 
ulnar vein. A new vein has grown from the external jugular down the 
anterior or radial border of the arm, and has united with the independ- 
ently formed interdigital veins. This is the cephalic vein of the adult. 
It is embryologically the second vein of the arm. 
Hochstetter states that the cephalic vein in rabbits develops toward the 
body from the back of the hand, connecting with the ulnar vein at the 
elbow, and later continuing up the arm to the external jugular vein. 
The preceding reconstructions of the rabbit agree better with Grosser’s 
description of the bats. He failed to find a stage in which the cephalic 
vein emptied into the ulnar. In the earliest specimen in which the 
cephalic vein was found, it connected with the external jugular vein. 
The cephalic vein of the 17-day rabbit is the chief vein of the limb, and 
has developed a branch which follows the radial artery, the deep radial 
. 
