PARKER AND TOZIER: POSTCARDINAL VEINS IN SWINE. 141 
which the accessory veins were developing, no trace of intercostals or 
intercostal anastomoses could be discovered, but the accessory veins 
grew at their posterior ends by a process that seemed like the formation 
of an opening through the tissues independent of any pre-existing blood- 
cavities. We therefore believe that Rathke was in error in ascribing to 
the non-cardinal parts of the azygos and hemiazygos veins in swine 
an origin from intercostal anastomoses. 
In justice to Rathke, however, it should be mentioned that longitudi- 
nal anastomosing vessels betwee. the intercostals do occur in embryonic 
pigs. We have never identified these in early stages, but their presence 
can be easily demonstrated in older embryos by means of celloidin in- 
jections that have been converted 
into corrosion preparations. In a 
pig about six centimeters long, the 
veins between the ninth and elev- 
enth intercostals, when thus prepared, 
and viewed from the dorsal side, are Bin Suet 
represented in Figure 5. From the — 
longitudinal hemiazygos (vn. hm'az.) 
pass off on the left the three inter- 
costals 9, 10, and 11; on the right, 
intercostal 11 and intercostal 9, to 
which intercostal 10 is attached by a 
longitudinal trunk (vn. az.), which 
probably represents a part of the 
once complete azygos. 
Each of the six intercostal veins TVN E 
mentioned gives off a short dorsal 
vessel, which opens into a zigzag longitudinal trunk (vn. lg.) of the 
corresponding side of the body. Thus the intercostals of a given side 
are put into communication with one another by a longitudinal anasto- 
mosing trunk. ‘fe right and left anastomosing trunks are moreover 
connected transversely, at regular and frequent intervals, in regions 
where their inwardly directed angles approach each other, thus pro- 
ducing a series of more or less hexagonal “ islands” bounded by blood- 
WN HWAZ =f- 
Fia. 5. The hemiazygos and connected veins from the region of the ninth to 
the eleventh intercostals in a pig about six centimeters long. Celloidin injection 
freed by artificial digestion. Dorsal view. X 10. vn.az„ azygos vein; vn. hm’az., 
hemiazy gos vein ; un. lg., longitudinal anastomosing vein; 9, 10, 11, respectively 
ninth, tenth, and eleventh intercostal veins of the left side. 
