68 H. D. SENIOR 
ramus communicans superius. The latter is longer and is 
recognizable as the ramus saphenus of the a. genu suprema. 
The difficulty in finding developmental stages in which the a. 
femoralis is present, but not yet united with the axial artery, 
coupled with the thinness of the wall of the femoral artery at 
this stage, indicates that the artery is one of extremely rapid 
growth. In a 12-mm. embryo slightly younger than the speci- 
men described (C. E. C., No. 3), reconstruction was begun under 
the impression that the femoral was absent. After more thorough 
study the artery was identified, bifurcated as in M. E. C., No. 
H 16, but much shorter. At this stage the a. femoralis has no 
branches, other than the terminal bifurcation already referred to. 
d. Stage of 14 mm. C. E. C., no. 5, figs. 4 and 9 D 
This stage is principally characterized by the participation of 
the a. femoralis in the blood supply of the leg and by the 
appearance of three branches of the axial artery. 
The r. communicans superius of the a. femoralis has joined the 
axial artery at the more proximal, of the two angular bends 
noticed in the preceding stage. The r. saphenus remains free 
and can be traced to the level of the knee joint. 
At the more distal bend of the axial artery there is now a 
branch, which passes to the extensor surface of the leg. This 
artery passes through the proximal end of the tibiofibular inter- 
space and takes a recurrent course toward the knee. The 
proximal part of the artery takes part in the formation of the 
adult a. tibialis anterior. It may be referred to as the ramus 
perforans cruris. The recurrent vessel continuing from the r. 
perforans cruris is the arteria recurrens tibialis anterior of the 
adult. 
The points marked upon the axial artery by means of the r. 
communicans superius and by the origin of the r. perforans 
cruris, respectively, may be used for the convenient subdivision 
of the vessel into three parts. The part upon the proximal side 
of the r. communicans superius will be referred to as the a. 
ischiadica and that upon the distal side of the r. perforans cruris 
