138 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
blood is conducted in the main through what is obviously the persistent 
azygos (vn. az.), though remnants of the hemiazygos occur between the 
ninth and tenth right intercostals, as well as between the eleventh and 
twelfth. 
Thus in the three types considered the anterior part of the system is 
always formed exclusively from the hemiazygos. The posterior part may 
( 
--YN.AZ 
-VN HAR 
A. B. C. 
FIGURE 4. 
be derived from the equally persistent azygos and hemiazygos (type one) 
or from a preponderant hemiazygos (type two) or finally from a pre- 
ponderant azygos (type three). 
Fic. 4. The hemiazygos and connected veins, showing three structural types. 
Raw gtareh injections. Ventral views. vn. az., azygos vein; vn. hm’az., hemi- 
azygos vein; 6, 10, 13, bases of the sixth, tenth, and thirteenth intercostal veins 
respectively. 
A. Type one, with equally persistent azygos and hemiazygos. From an em- 
bryonic pig about seven centimeters long. X 3. 
B. Type two, with preponderant hemiazygos. From an embryonic pig about 
eleven centimeters long. X 2. 
C. Type three, with preponderant azygos. From an embryonic pig about 
twenty centimeters long. Natural size. 
