366 MALL. 
the subclavian artery. In so doing the subclavian is caught in 
the sympathetic cord in its earliest stage, while the greater 
portion of the cord is developed on the dorsal side of the artery. 
The portion of the sympathetic which from the first lies on the 
ventral side of the subclavian becomes the ansa subclavia. 
The descent of the heart into the thorax on the inside with 
the descent of the arm over the clavicle on the outside causes 
great tension on the upper intercostal arteries, and favors the 
new formation of blood vessels in a more direct line. This is 
the reason why the main branch of superior intercostal is a 
secondary and direct artery from the subclavian. 
Résumé. — The permanent abdominal walls, then, are formed 
by its various structures growing from the ventral plate into 
the membrana reuniens. The muscles grow as buds from the 
myotomes, and their original segmental nature is retained in 
great part by the intercostal and abdominal muscles. Each 
segment in shifting retains its original nervous connection, so 
that the origin of each segmental muscle is indicated by its 
nervous supply. 
The segmental arteries soon unite at their tips, much after 
the fashion of the formation of the vertebral, to form the deep 
epigastric and internal mammary arteries. This arterial bridge 
is complete while it still lies on the lateral side of the body, 
and then obtains its definite position by shifting around to the 
ventral middle line of the body hand in hand with the ribs and 
rectus abdominis muscle. 
In pigs’ embryos the milk line lies immediately over the 
rectus and the arterial arch, and it shifts towards the middle 
line with them. Not only can this be determined by sections 
but also by observing live embryos. In the latter instance a 
cutaneous vessel is seen along the mammary, which belongs to 
the internal mammary and deep epigastric arteries. So the 
rectus, milk line, and the arterial arch with its cutaneous 
branches mark the border of the ventral plate as it invades the 
membrana reuniens. _ 
JoHNs HopkINS UNIVERSITY, 
September 28, 1897. 
