Joseph Marshall Flint 431 
In a pig 18 centimeters long the main submaxillary vessels and sub- 
maxillary duct are now some- 
what separated. Arteries and 
veins are distinctly seen in the 
plexus embracing the ductus 
submaxillaris. These are de- 
rived from its vasa comites. The 
ramification has not increased 
so much in number of orders as 
in the number of branches. The 
arteries still preserve their ia- 
dividuality but a duplication of 
veins is observed as ducts in- 
: 1 7 5 ne Fie. 7. Submaxillary gland of pig’s embryo 18 
crease in size. Here and there centimeters long. Same method of preparation 
q 7 rat and magnification as Fig.5. The arteries and 
one finds not infrequently a venae comites are distinctly seen. These may 
7 +] 9 mad follow as faras the terminal arterioles which 
vein looping around the arteries arenow forming those of the lobular type. 
1 + x Little capillary clusters with their arterioles 
and vcr embracing the ducts. and venules represent the secondary or ulti- 
At this period vessels of the lob- Horace The plexus about the ducts is 
ular type have just been formed 
and the capillary piexus around the alveoli is very sharp and distinct. 
Anastomoses have been established between the capillary systems of 
adjacent alveolar groups. This forms for the first time in the history of 
the organ the final arrangement of the circulation in the lobule, although 
representing it in a very simple form. Here and there the connections 
between the alveolar circulation and the circulation of the capsule are 
seen, while, for the first time, perforating vessels leave the lobules and 
ramify in septa of the first and second orders. These appear best in Prus- 
sian blue specimens where the injection is complete. Compared with other 
organs, the amount of syncytium from which the fibrillar and cellular 
parts of the submaxillary framework are derived is proportionately 
excessive to the quantity of cells forming the primitive ducts which are 
destined to yield all of the epithelial elements of the gland. In all of 
the early stages, the blood-vessels are confined to the immediate neigh- 
borhood of the ducts, while the syncytium has none. As this syncytium 
is transformed into strands and septa, they receive a vascular supply of 
their own, which is not well shown until the pig reaches an age indicated 
by a nape-breech measurement of 18 centimeters. The interspaces have 
now attained a definite size and blood-vessels derived from the vasa 
comites of the main ducts leave the plexus and ramify in the substance 
of the connective tissue, here and there giving off arteries to supply the 
