Frederic T. Lewis PRG 
arch produced a structure similar to the superior part of the thymus 
but which remained behind the thyroid gland. As already stated, in 
the 14-mm. pig this mass has apparently united with the superior part of 
the thymus. In an embryo of 24 mm. the thymus consists of the 
approximated and proliferated ends of the ventral arms of the third 
clefts. From each of these a slender cord passes upward and backward 
to join the considerable cell mass near the vagus. This connection is 
broken, and the.small upper part has been variously called the carotid 
gland, the parathyroid body or, more recently, the epithelial body 
(Maurer, 02). 
The right lung is figured in Plate III. Its elongated condition as com- 
pared with the human lung is noteworthy. Above the bifurcation of 
the trachea there is a budding bronchus which is to supply the upper 
lobe of the right lung. No corresponding branch is found on the oppo- 
site side. This asymmetry of the lungs, described by Aeby, bas been 
found well developed in the lowest of existing mammalia (Wiedersheim, 
02, p. 484). With this, its early embryonic appearance is in full 
accord. Keibel, 97, found the tracheal bronchus in a 9.6-mm. embryo; 
in the Harvard Collection it is well developed at 9.0 mm. 
The stomach is already a pig’s stomach, possessing in its cardiac por- 
tion a well marked diverticulum. 
The liver comprises four large lobes which are visible before the 
embryo is sectioned. Along its lower surface there extends a pouch, 
exceeding in diameter the intestine from which it arises and into which 
it empties. Its cylindrical epithelium is quite unlike that of the he- 
patic cylinders, but resembles somewhat the intestinal mucosa. This 
large diverticulum ends blindly, its terminal portion being separated 
from the liver by mesenchyma. Sometimes a knob-like bud is found 
on its surface. Nearer the intestine these buds are more numerous. 
Some of them terminate in hepatic cylinders; others end blindly, or are 
found as detached cysts in the liver. Later all but one of these hepatic 
ducts are obliterated, and the diverticulum into which it empties 
has become in part the cystic duct and in part the gall-bladder. 
Brachet, 96, p. 666, describes similarly the development of the rabbit’s 
biliary ducts. There is first a single intestinal diverticulum, from 
the proximal two-thirds of which the hepatic cylinders proliferate, and 
of which the quiescent distal part is retained as the gall-bladder. From 
its embryological history, it is to be expected that the hepatic ducts 
possess glands “resembling those of the gastric cardia” and that in the 
distended gall-bladder such glands should be absent. 
The pancreas consists of two closely applied divisions. The ventral 
