THE CIRCULATORY SYSTEM 183 
artery known as the common iliac is the first formed of the 
posterior limb, and that it arises as a segmental vessel of the 
aorta. 
The artery which, in the embryo Mammal, including Man, 
runs into the developing posterior limb bud, does not directly 
become the arteria femoralis of the adult. It accompanies the 
ischiadic [or crural] nerve in its distribution; on the posterior 
side of the limb it runs down to the bend of the knee, and from 
this point is continued into the upper part of the thigh. This 
artery should be called the ischiadic [or crural] as it corresponds 
with the vessel of the same name in most Birds, and with the 
principal vessel of the hind-limb in Reptiles and Amphibians. 
“The femoral artery develops later as a branch of the iliac. 
At first 1t spreads only over the inner or ventral portion of the 
thigh ; it, however, soon grows rapidly in a distal direction, along 
the inner surface of the cartilaginous femur, to the bend of the knee, 
where it unites with the ischiadic artery. The femoral artery 
thus formed rapidly increases in size, while that section of the 
ischiadic related to the upper leg degenerates. It is thus 
that the definitive condition is attained; and but a short vestige 
of the arteria ischiadica persists in the adult, as the “ischiadic” 
or “inferior gluteal” (Hochstetter). Mechanical causes may have 
perhaps brought about this change in the principal artery of the 
hind-limb in the ancestors of Mammals, but we have no clear 
knowledge on the subject. 
In no other part of the body are the variations in the arteries 
so frequent as in the fore-limb, especially in the hand. The 
arteries of the foot present numerous variations, and, in correla- 
tion with the variations of the skeleton and musculature, 
some of these may be classed as progressive and others as 
retrogressive. 
Where a supracondyloid process of the humerus exists (cf. 
ante, p. 78) the brachial artery lies behind it. The latter is 
thus covered by the head of the pronator teres muscle which 
extends upwards, and the condition resembles that of those 
Mammals in which the brachial artery and median nerve pass 
through an invariably developed foramen supracondyloideum.! 
A comparison of the arteries of the hand with those of the 
foot shows that there are in the hand two palmar arches, a 
to the recent series of very careful studies by Hochstetter, published in the Morpho- 
logisches Jahrbuch. 
' For further details on this point, cf. Ruge, Morpholg. Jahrb., Bd. ix. p. 329. 
