440 MALL. EVOL. XIE 
cervical nerve ; Cadiat and His recognized the mass of tissue 
in the embryo which is destined to give rise to the diaphragm ; 
Uskow and Ravn studied more carefully the separation of the 
body cavities from one another; and the wandering of the organs 
was emphasized by Uskow. 
It is now no great task for me to give the development of 
the diaphragm in the human embryo, for I have at my dis- 
posal excellent sections, as well as definite knowledge of the 
anatomy of the surrounding organs contributed by the above- 
mentioned authors. 
While the embryo is still straight it is very easy to locate the 
various organs and their relations to one another, but through 
their shifting and the flexion and extension of the embryo the 
relations are constantly changing, and one must not rely too 
much upon sections, or else erroneous impressions will often 
be obtained. At first the heart is upon the oral and dorsal 
side of the septum transversum, then on its ventral side, and 
finally again on its dorsal side. At first the lungs are on the 
dorsal side of the heart, then on the lateral side, and finally 
also on the ventral side of it. At first the liver is on the aboral 
side of the septum transversum in the head of the embryo, then 
on the dorsal side of it in the cervical region of the embryo, 
then as the liver is descending in its excursion it is transferred 
to the ventral side of the septum and extends into the sacral 
region. At first the Wolffian body extends high into the tho- 
racic region of the embryo, but while it is degenerating and the 
diaphragm descends, the upper part of the posterior cardinal 
vein remains, while the lower part is incorporated with its vena 
cava inferior, as shown by Hochstetter.1 As the Cuvierian 
ducts and cardinal vein descend into the thorax, the segmental 
veins entering the cardinal veins are gradually shifted, so that 
veins which originally emptied into the posterior cardinal now 
empty into the anterior cardinal. While the whole process is 
taking place the arteries arising from the descending aorta also 
shift, as I have shown in a previous communication.2 At that 
time my collection of human embryos was very limited, and it 
1 Hochstetter: Morph. Jahr., Bd. 20, p. 563. 
2 Mall: Journ. of Morph., vol. V, p. 472. 
