of Single Hypogastric artery in the Human Foetus. 335 
Finally they unite to form the inferior vena cava. In a sense, 
therefore, two inferior venae cavae may be said to exist here. 
The ground has now been cleared for gathering together the 
various pieces of evidence bearing upon the problem in hand. 
This is somewhat simplified by considering the connexions of the 
several arteries when viewed from one side only, as represented in 
Fig. 13. Ventral and dorsal divisions of the aorta diverge from 
their point of origin, but their terminal branches come into 
close proximity and probably anastomose in the region of the 
sacro-iliac synchondrosis. Such an arrangement is still more 
diagram matically shewn in Fig. 14, which should be compared with 
the normal arrangement represented in Fig. 15. 
Fig. 14. Sketch to illustrate the interpretation of the abnormal arrangement 
of the abdominal arteries in specimen F. 
My interpretation of the conditions found in specimen F is 
therefore that : 
(a) The normal so-called secondary caudal arch has been 
interrupted on that side which is formed by the primitive dorsal 
aorta. The cause of the interruption is bound up with those 
which have determined the other malformations of the caudal 
end of the trunk and of the limbs. 
(b) Concurrently with this interruption, an anastomosis has 
been opened up between a segmental splanchnic vessel (one of the 
omphalo-meseraic series), and one of the normal vitelline branches 
of the hypogastric artery. This anastomotic channel has been 
