Joseph Marshall Flint 425 
into the terminal vein. Each lobule is composed of a series of such 
units. Even another larger unit might be constructed from the circu- 
lation embraced between the sublobular artery and the sublobular vein, 
supplying groups of lobules that have definite relations with the second- 
ary septa. The ultimate lobular unit might well be considered the 
least, while the primitive lobule would be the greatest common struc- 
tural divisor of the submaxillary gland. The smaller terminal units 
are comparable to the conditions of the circulation in such glands as 
the stomach and adrenal where cell complexes having definite relations 
with larger bands of connective tissue do not exist. 
CIRCULATION ABOUT THE DUCTS. 
The ductus submaxillaris is embraced by a rich supply of arteries 
derived from the Aa. principales, branches of which run in a recurrent 
Fic. 2. Blood-vessels about the ductus submavxillaris in a pig 26 centimeters long 
showing the arterial, venous and capillary plexuses: arteries light, veins and capil- 
laries dark. 
direction along the walls of the ducts as far as the hilus. These arteries 
may anastomose with some frequency (Fig. 2), although the plexus 
formed by them is not a rich one. They are distributed around the sur- 
face of the duct and give off terminal branches which sink to the region 
just around the base of the duct epithelium and terminate in a capillary 
plexus formed of small, irregular, polygonal meshes. Through the conflu- 
ence of the capillaries, numerous venules are derived which empty into 
large veins forming an irregular venous plexus about the duct. The cali- 
ber of these veins is larger than the arteries, and the meshes formed by 
them are irregular and polygonal. The venous plexus lies below the 
arterial and from a convergence of its elements larger veins are formed 
