ARTERIES OF HUMAN LOWER EXTREMITY 83 
At the stage of 20 mm. (fig. 10, A) blood traverses the pop- 
liteal region to reach the r. perforans cruris through the original 
channel, namely the a. poplitea profunda. The a. poplitea 
superficialis is longer than at the stage of 18 mm., having in- 
creased in length at the expense of the aa. tibialis posterior 
superficialis and peronaea posterior superficialis. 
At the stage of 22 mm. (fig. 10, B), a junction between the 
developing a. peronaea and the distal part of the a. poplitea 
Fig. 10 Three reconstructions, each showing a sagittal segment (0.25 mm. 
thick) from the left leg of an embryo of the length indicated. Lateral aspect. 
xX 19. A, 20 mm.; B, 22 mm.; C, 24.8mm. The tibia appears in all cases. P. 
indicates the position of the m. popliteus. c.m., a. communicans media; g. 7. m., 
a. genu inferior medialis; g. m., a. genu media; 7., a. interossea; 7.m., interosseous 
‘membrane; p., a. poplitea; p.c., a. perforans cruris; p. d., a. tibialis anterior, pars 
distalis; p. p., a. poplitea profunda; p. s., a. poplitea superficialis; per., a. 
peronaea; 7. a., a. recurrens tibialis anterior; r. p., a. recurrens tibialis posterior; 
t. a., a. tibialis anterior; ¢. p. s., a. tibialis posterior superficialis. 
profunda has been effected by the development of the r. com- 
municans medius. Blood may now pass from the proximal part 
of the a. poplitea profunda to the a. tibialis anterior, pars dis- 
talis by two routes: 1) anterior to the m. popliteus, by way of 
the distal part of the a. poplitea profunda and r. perforans cruris, 
or 2) posterior to the m. popliteus, by way of the a. poplitea 
superficialis, developing a. peronaea, r. communicans medius, a. 
poplitea profunda, and r. perforans cruris. 
