118 Development of the Veins in the Limbs of Rabbit Embryos 
them is uncertain. The femoral and brachial veins ‘** show no agreement 
either in position or in origin” (p. 35). 
These conclusions clearly depend upon the serial homology of the limbs. 
If we should accept the idea of inverse homology, advocated by Wilder, 
Wyman, and others, according to whom the thumb is comparable with the 
little toe, and the radial border with the ulnar, then conclusions almost the 
reverse of Hochstetter’s would be expected. A third basis for comparison 
Ul. UI. 
Fi. 
\ 
A 
DracRAM 1. Anterior view of the arm and leg in their three stages of 
venous development. In Stage 1, a and A show the arm and leg, respectively, 
before rotation; b and B, after rotation. The primitive ulnar and fibular 
veins are in solid black. The secondary cephalic and sciatic veins are drawn 
as double lines, and the tertiary brachial and femoral veins have transverse 
shading. The black lines in contact with the secondary and tertiary vessels 
indicate the portions of those veins which are formed from the primitive 
vessels of Stage 1. 
B 
STAGE 1. STAGE 2. STAGE 3. 
is supplied by the familiar rotation theory. According to it, the limbs 
are at first serially homologous. The thumb and great toe, the ulnar and 
fibular borders correspond. The external surfaces of both limbs are to 
be extensor and the inner surfaces flexor. Later a rotation of approxi- 
mately 90° occurs in both limbs, but in opposite directions. The ex- 
tensor surface of the arm becomes posterior, and that of the leg becomes 
anterior. The knee and elbow are thus brought to bend in opposite 
directions. The foot is rotated with the leg and its extensor surface 
