ARTERIES OF HUMAN LOWER EXTREMITY '85 
origin of the a. peronaea from the termination of the a. poplitea 
to a point upon the a. tibialis posterior. : 
After the formation of the a. tibialis posterior has been com- 
pleted by the occurrence of these changes the vessel still retains 
its original relation to the n. tibialis. The relations between 
the a. poplitea and the n. tibialis also differ from those of the 
adult. 
The entire a. poplitea lies upon the medial side of the n. 
tibialis. The a. tibialis posterior crosses the medial side of the 
nerve to gain its posterior aspect upon which it runs until it 
ends behind the medial malleolus. The relations of the aa. 
poplitea and tibialis posterior to the n. tibialis have been 
thoroughly studied up to the stage of 22 mm. They seem to 
remain unaltered in the oldest serially cut embryo which has 
been examined in this regard. It is C. I. E. C., no. 1134, which 
measures 33.5 mm. . 
It is not difficult to see how an agency capable of moving 
the termination of the a. poplitea across the anterior aspect of 
the n. tibialis from the medial to the lateral side would produce 
a condition differing little from that normally encountered in 
the adult. Since the knee is flexed throughout intrauterine life 
it would seem that the modification of the relative positions of 
the arteries and nerve might depend upon the straightening of 
the n. tibialis which occurs at birth. In order to put the matter 
to the test, a foetus of 7.9 cm. was dissected.!2 The rela‘ions, 
however, were found to be identical with those of the adult. 
Apart from the study of a few special points, this investigation 
has not extended beyond the stage of 22 mm. At that period 
all the vessels of the adult limb are present with the exception 
of two of the three aa. perforantes, which usually arise from the 
adult a. profunda femoris, the a. circumflexa femoris medialis, 
and the a. obturatoria. At the stage of 22 mm. two obturator 
veins are present in C. E. C., no. 1, one of these is tributary 
to the v. hypogastrica, the other to the v. femoralis. 
The leading features in the process of the arterial development 
of the limb are indicated in figure 11. 
122 For this dissection and for many others made upon various mammals, I 
wish to express my indebtedness to Mr. B. Spector. 
