420 The Submaxillary Gland 
enter the hilus of the organ with the duct, but join the latter a short 
distance after it penetrates the gland and take up immediately the close 
relations which are observed throughout the developmental and adult 
periods of life. The veins follow the arteries throughout their course. 
In the pig, however, the duct is joined by the blood-vessels almost imme- 
diately after their passage through the hilus, even before branches of 
the first order are given off. The relationship between the duct and 
vascular systems is absolutely constant and dates from the earliest em- 
bryonic history of the organ. 
Inasmuch as the nomenclature of the blood-vessels is taken from 
that of the ducts, a short account of the latter may simplify the 
description of the vascular system. In pigs, the distribution of the 
ducts is not unlike that in man, although in the former it is 
somewhat more regular. In man the ductus submaxillaris enters 
the hilus of the gland and almost immediately breaks up into 
branches of the first order. These run a very short distance and then 
terminate in a secondary system, forming interlobular ducts that ramify 
extensively throughout the gland. From the latter are derived a set 
of sublobular ducts. These divide once or twice and then terminate in 
lobular ducts which, entering the hilus of the ultimate lobules, at once 
exhaust themselves in the extensive ramifications that form the intra- 
lobular ducts and radiate from the hilus to the periphery of the lobule. 
They terminate in a short duct of slightly smaller caliber termed the 
intercalary portion connecting them directly with the secreting alveoli 
of the gland. ‘The intercalary ducts are usually considered as having a 
much smaller caliber than the ducts of the next lower order. This, how- 
ever, is not the case, as their lumen, as shown by corrosion preparations, 
is only slightly smaller than those just preceding. This mistaken im- 
pression probably arose from the consideration of the ducts when clothed 
with their epithelium. The total diameter of the intermediate ducts 
is much smaller, because the intralobular ducts on one side are lined with 
columnar epithelium and the alveoli have etther high mucous or serous 
cells on the other, while the intercalated portions of the duct between 
them have only flattened epithelial cells for their walls. Running in 
the thick processes of fasciculated connective tissue that form the inter- 
lobular spaces, are the blood-vessels that always accompany the ducts. 
In one way, the interlobular spaces of the salivary glands have a certain 
resemblance to those of the liver except that the former have two veins 
instead of the single branch of the portal system found in the hepatic 
interspaces. 
In describing the blood-vessels of the adult organ, it is convenient to 
divide them into three systems: 
