ARTERIES OF HUMAN LOWER EXTREMITY 71 
e. Stage of 17.8 mm. H. E. C., no. 839, figs. 5 and 9 E 
During the preceding stages of development the arterial retia 
of the foot have received their blood supply exclusively through 
the a. interossea; the reta plantare directly, and the rete dorsale 
by means of the r. perforans tarsi. The mesenchymal skeleton 
of the foot is now definitely circumscribed, and it is plain that 
the latter vessel reaches the dorsum by way of the tarsal sinus. 
The arterial retia of the foot lie in close contact with the tarsus 
and metatarsus and represent the following vessels of the adult 
circulation—the arcus plantaris and its articular branches, the 
aa. tarseae mediales and laterales, the a. arcuata, the aa. meta- 
tarseae and digitales (both dorsal and plantar), and the rami 
perforantes (including the ramus plantaris profundus). 
The present stage is characterized by the presence of four 
arteries which traverse the leg for the supply of the sole. The 
a. interossea is still present, the aa. tibialis posterior superficialis 
and peronaea posterior superficialis have formed their definitive 
connections, and a new vessel, the a. tibialis anterior, pars 
distalis, has arisen. 
The a. tibialis posterior superficialis and the a. peronaea 
posterior superficialis preserve in the leg the same relations to 
the n. tibialis as obtained in the preceding stage. At the ankle 
the medial terminal branch of the a. peronaea posterior super- 
ficialis has traversed the fork formed by the diverging plantar 
nerves to join the a. tibialis posterior superficialis. The lateral 
terminal branch of the same artery has reached the lateral side 
of the sole to join the plantar arterial rete. The connection thus 
formed between the a. tibialis posterior superficialis and the 
rete plantare becomes the a. plantaris lateralis of the adult foot. 
At the present stage of development it receives blood from two 
sources. 
° The greatest total length of this embryo, measured in formalin, was 17.8 mm. 
In 80 per cent alcohol it measured 13.6 mm. It has been described by Thyng as a 
17.8 mm. embryo (Am. Jour. Anat., vol. 17, p. 31), and referred to by Thyng 
(Am. Jour. Anat., vol. 7, p. 489) and by Thyng and Lewis (Am. Jour. Anat., vol. 7, 
p. 505) as an embryo of 13.6 mm. The distribution of the arteries of the lower 
extremity resembles that of other embryos of about 15 or 16 mm. 
