ARTERIES OF HUMAN LOWER EXTREMITY 91 
A. peronaea posterior superficialis. The course of this em- 
bryonic artery is described on pages 70 and 74. The main stem 
of the vessel is present at the stage of 14 mm., its terminal 
branches form their definitive connections at a stage of 15 or 16 
mm. 
The proximal part of the a. peronaea posterior superficialis 
unites with the a. tibialis posterior superficialis to form the .a. 
poplitea superficialis and the part of the a. tibialis posterior 
above the root of the a. peronaea. A more distal portion persists 
as the first part of the a. peronaea, and a still more distal portion 
enters slightly into the formation of the fourth part of that 
vessel. 
The terminal branches of the a. peronaea posterior super- 
ficialis form the adult a. plantaris lateralis. The r. calcaneus 
medialis of the latter artery represents the end of the stem of 
the parent vessel. The r. calcaneus lateralis, which arises from 
the a. peronaea posterior superficialis shortly before the stage 
of 18 mm., persists to form the major portion of the fourth part 
of the a. peronaea (p. 79). 
A. plantaris lateralis. The proximal part of this artery 
represents the medial terminal branch of the a. peronaea pos- 
terior superficialis (p. 71), which unites with the a. tibialis 
posterior superficialis. The distal part represents the lateral 
terminal part of the same vessel. 
Branches. The r. caleaneus medialis represents the terminal 
portion of the main trunk of the embryonic a. peronaea posterior 
superficialis. The arcus plantaris and all its branches are de- 
rived from the embryonic rete plantare. 
A. plantaris medialis. This artery is the distal portion of the 
embryonic a. tibialis posterior superficialis. It is marked off 
- from the remainder of that vessel by the medial terminal branch 
of the embryonic a. peronaea posterior superficialis. 
A. poplitea. The part of this artery above the origin of the a. 
genu inferior medialis represents a surviving portion of the 
embryonic a. poplitea profunda (p. 73). The part lying upon 
the posterior surface of that muscle represents the embryonic a. 
poplitea superficialis. The proximal portion of the a. genu 
inferior medialis is derived from the a. poplitea profunda. 
