ARTERIES OF HUMAN LOWER EXTREMITY io 
to the region of the hiatus tendineus upon the lateral side of the 
n. tibialis. The n. peronaeus lies immediately upon its lateral 
side. 
In a general way the aa. poplitea profunda and interossea 
and their branches have the same arrangement as in the pre- 
ceding stage. The exact course taken by these vessels can now 
be clearly recognized, since it is possible to identify the individual 
muscles of the limb. 
The a. poplitea profunda runs between the m. popliteus and 
the tibia. At the proximal border of the muscle the artery 
gives off the a. genu media and a short trunk which is being 
formed by the progressive union of the proximal ends of the aa. 
tibialis posterior superficialis and the a. peronaea posterior super- 
ficialis. This short trunk, which lies upon the posterior surface 
of the m. popliteus, may now be called the a. poplitea super- 
ficialis. It forms the distal part of the a. poplitea of the adult. 
A short distance below the origin of the a. poplitea superficialis 
there arises the a. genu inferior medialis. 
The a. interossea passes down the leg between the m. tibialis 
posterior and the interosseous membrane. Just above the 
medial malleolus it gives off a branch which passes around the 
posterior to the medial side of the tibia, the ramus coronarius 
of the medial malleolus (Hyrtl).1° At the malleolus the a. 
10 In this vessel lies, according to Hyrtl, the key to the deep supramalleolar 
anastomosis (i.e., the r. communicans) between the a. peronaea and the a. 
tibialis posterior. The r. coronarius is regarded by Hyrtl as primarily passing 
from the a. peronaea around the medial side of the tibia to unite with the a. 
tibialis anterior. By means of a secondary connection occurring between the r. 
coronarius and the a. tibialis posterior, the former vessel eventually becomes 
converted into an anastomosing chain in which the aa. malleolaris anterior 
medialis, malleolaris posterior medialis and r. communicans are the named 
components. At thestage of 18 mm. of this series the r. coronarius arises from the 
part of the a. interossea which persists to take part in the formation of the adult 
a.peronaea. It runs, at this stage, as at the stage of 22 mm., toward the a. tibialis 
anterior as described by Hyrtl, and would, no doubt, eventually join it. Since 
in both these stages the a. tibialis posterior is situated upon a plane superficial 
to that occupied by the r. coronarius, no junction of the vessels in question has 
occurred. There can be little doubt, however, that Hyrtl has interpreted the 
nature of the r. coronarius correctly. His views upon this subject, which were 
derived from an extensive study of the normal and abnormal conditions found 
in adult legs, have been of the greatest assistance in the interpretation of the 
conditions obtaining during development. 
